[ResponseOps][Cases] De-duplicate assignees object name (#194359)

## Summary

Common client generators fail with the current Kibana spec due to
duplicate type names used within the Case API.

```
❯ go run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen -package=kibana -generate=types,client -o ../generated/kibana.gen.go ../kibana-openapi-source.yaml
error generating code: error generating type definitions: error generating code for type definitions: duplicate typename 'CasesAssignees' detected, can't auto-rename, please use x-go-name to specify your own name for one of them
exit status 1
```


### Checklist

Delete any items that are not applicable to this PR.

- [x] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [x]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [x] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [x] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [x] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [x] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [x] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

oas_docs/output/kibana.staging.yaml

@@ -6948,7 +6948,7 @@ paths:
         feature privileges, depending on the owner of the cases you're seeking.
       operationId: findCasesDefaultSpace
       parameters:
-        - $ref: '#/components/parameters/Cases_assignees'
+        - $ref: '#/components/parameters/Cases_assignees_filter'
         - $ref: '#/components/parameters/Cases_category'
         - $ref: '#/components/parameters/Cases_defaultSearchOperator'
         - $ref: '#/components/parameters/Cases_from'
@@ -24388,7 +24388,7 @@ components:
       schema:
         example: 09f0c261e39e36351d75995b78bb83673774d1bc2cca9df2d15f0e5c0a99a540
         type: string
-    Cases_assignees:
+    Cases_assignees_filter:
       description: >
         Filters the returned cases by assignees. Valid values are `none` or
         unique identifiers for the user profiles. These identifiers can be found

oas_docs/output/kibana.yaml

@@ -6684,7 +6684,7 @@ paths:
         feature privileges, depending on the owner of the cases you're seeking.
       operationId: findCasesDefaultSpace
       parameters:
-        - $ref: '#/components/parameters/Cases_assignees'
+        - $ref: '#/components/parameters/Cases_assignees_filter'
         - $ref: '#/components/parameters/Cases_category'
         - $ref: '#/components/parameters/Cases_defaultSearchOperator'
         - $ref: '#/components/parameters/Cases_from'
@@ -16415,7 +16415,7 @@ components:
       schema:
         example: 09f0c261e39e36351d75995b78bb83673774d1bc2cca9df2d15f0e5c0a99a540
         type: string
-    Cases_assignees:
+    Cases_assignees_filter:
       description: >
         Filters the returned cases by assignees. Valid values are `none` or
         unique identifiers for the user profiles. These identifiers can be found

x-pack/plugins/cases/docs/openapi/bundled.json

@@ -179,7 +179,7 @@
         ],
         "parameters": [
           {
-            "$ref": "#/components/parameters/assignees"
+            "$ref": "#/components/parameters/assignees_filter"
           },
           {
             "$ref": "#/components/parameters/category"
@@ -1897,7 +1897,7 @@
         },
         "example": "d4e7abb0-b462-11ec-9a8d-698504725a43"
       },
-      "assignees": {
+      "assignees_filter": {
         "in": "query",
         "name": "assignees",
         "description": "Filters the returned cases by assignees. Valid values are `none` or unique identifiers for the user profiles. These identifiers can be found by using the suggest user profile API.\n",

x-pack/plugins/cases/docs/openapi/bundled.yaml

@@ -112,7 +112,7 @@ paths:
       tags:
         - cases
       parameters:
-        - $ref: '#/components/parameters/assignees'
+        - $ref: '#/components/parameters/assignees_filter'
         - $ref: '#/components/parameters/category'
         - $ref: '#/components/parameters/defaultSearchOperator'
         - $ref: '#/components/parameters/from'
@@ -1230,7 +1230,7 @@ components:
           minItems: 1
           maxItems: 100
       example: d4e7abb0-b462-11ec-9a8d-698504725a43
-    assignees:
+    assignees_filter:
       in: query
       name: assignees
       description: |

x-pack/plugins/cases/docs/openapi/paths/api@cases@_find.yaml

@@ -8,7 +8,7 @@ get:
   tags:
     - cases
   parameters:
-    - $ref: '../components/parameters/assignees.yaml'
+    - $ref: '../components/parameters/assignees_filter.yaml'
     - $ref: '../components/parameters/category.yaml'
     - $ref: '../components/parameters/defaultSearchOperator.yaml'
     - $ref: '../components/parameters/from.yaml'