Saved Object Mapping for Entity Source Sync Configuration (#219680)

## Summary

This PR introduces a new Saved Object mapping for Monitoring Entity
Source Configurations to support Privileged User Monitoring.

### ✅ Implemented
* Saved object mapping schema aligned with the [current
spec](https://docs.google.com/document/d/1-c6A82p2CCjYz8Mb6tL6R7BXXemQ4mpWZliKqki0SWo/edit?tab=t.0#heading=h.4axxr154e1lc)
* DescriptorClient to handle saved object methods
* OpenAPI schema and generated types
* Implemented Data Client - SO operations exposed via GET and POST API
* Created route and registered with privmonRoutes
* Data Client Unit Testing
* Rename typename of "monitoring_entity_source-sync" ->
"entity-analytics-monitoring-entity-source"

[Figma
](https://www.figma.com/board/yBr1pBDGu4JqNxb5ZrULtk/MonEntitySourceSyncTask?node-id=0-1&p=f&t=4hQaGsdvOpghi4QS-0)-
currently working in the pink box


## Testing Steps: 
1. privilegeMonitoringEnabled: true - set this flag
2. From Dev tools - create a saved object via POST (below) and view this
saved object via GET (also below):


```
POST kbn:/api/entity_analytics/monitoring/entity_source
{
  "type": "some-type-here",
  "name": "name-here",
  "managed": false,
  "indexPattern": "logs-*",
  "enabled": true,
  "integrationName": "Okta",
 "matchers": [
    {
      "fields": ["user.role"],
      "values": ["admin"]
    }
  ],
  "filter": {}
}

```
**Expected output:** 
``` 
{
  "type": "some-type-here",
  "name": "name-here",
  "managed": false,
  "indexPattern": "logs-*",
  "enabled": true,
  "integrationName": "Okta",
  "matchers": [
    {
      "fields": [
        "user.role"
      ],
      "values": [
        "admin"
      ]
    }
  ],
  "filter": {}
}
```
GET Example
```
GET kbn:/api/entity_analytics/monitoring/entity_source
```
Output for get, expected to be the same as that for POST.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

packages/kbn-check-mappings-update-cli/current_fields.json

@@ -309,6 +309,19 @@
     "schemaVersion"
   ],
   "enterprise_search_telemetry": [],
+  "entity-analytics-monitoring-entity-source": [
+    "enabled",
+    "error",
+    "filter",
+    "indexPattern",
+    "integrationName",
+    "managed",
+    "matchers",
+    "matchers.fields",
+    "matchers.values",
+    "name",
+    "type"
+  ],
   "entity-definition": [
     "description",
     "filter",
@@ -828,6 +841,19 @@
     "job.job_id",
     "model_id"
   ],
+  "monitoring-entity-source": [
+    "enabled",
+    "error",
+    "filter",
+    "indexPattern",
+    "integrationName",
+    "managed",
+    "matchers",
+    "matchers.fields",
+    "matchers.values",
+    "name",
+    "type"
+  ],
   "monitoring-telemetry": [
     "reportedClusterUuids"
   ],

packages/kbn-check-mappings-update-cli/current_mappings.json

@@ -1059,6 +1059,37 @@
     "dynamic": false,
     "properties": {}
   },
+  "entity-analytics-monitoring-entity-source": {
+    "dynamic": false,
+    "properties": {
+      "enabled": {
+        "type": "boolean"
+      },
+      "error": {
+        "type": "keyword"
+      },
+      "filter": {
+        "dynamic": false,
+        "type": "object"
+      },
+      "integrationName": {
+        "type": "keyword"
+      },
+      "managed": {
+        "type": "boolean"
+      },
+        "matchers": {
+        "dynamic": false,
+        "type": "object"
+      },
+      "name": {
+        "type": "keyword"
+      },
+      "type": {
+        "type": "keyword"
+      }
+    }
+  },
   "entity-definition": {
     "dynamic": false,
     "properties": {