[DOCS] Add minimal synthetic APIs (#214518)

Co-authored-by: Colleen McGinnis <colleen.j.mcginnis@gmail.com>

oas_docs/overlays/kibana.overlays.yaml

@@ -127,6 +127,13 @@ actions:
         * [Short URLs](https://www.elastic.co/guide/en/kibana/current/short-urls-api.html)
 
         Warning: Do not write documents directly to the `.kibana` index. When you write directly to the `.kibana` index, the data becomes corrupted and permanently breaks future Kibana versions
+  - target: '$.tags[?(@.name=="synthetics")]'
+    description: Add tag info
+    update:
+        x-displayName: Synthetics
+        externalDocs:
+          description: Synthetic monitoring
+          url: https://www.elastic.co/guide/en/observability/current/monitor-uptime-synthetics.html
 # Remove extra tags from operations
   - target: "$.paths[*][*].tags[1:]"
     description: Remove all but first tag from operations

oas_docs/scripts/merge_ess_oas.js

@@ -31,6 +31,7 @@ const { REPO_ROOT } = require('@kbn/repo-info');
       `${REPO_ROOT}/x-pack/solutions/observability/plugins/apm/docs/openapi/apm/bundled.yaml`,
       `${REPO_ROOT}/x-pack/solutions/observability/plugins/slo/docs/openapi/slo/bundled.yaml`,
       `${REPO_ROOT}/x-pack/solutions/observability/plugins/uptime/docs/openapi/uptime_apis.yaml`,
+      `${REPO_ROOT}/x-pack/solutions/observability/plugins/synthetics/docs/openapi/synthetic_apis.yaml`,
 
       // Security solution
       `${REPO_ROOT}/x-pack/solutions/security/plugins/security_solution/docs/openapi/ess/*.schema.yaml`,

x-pack/solutions/observability/plugins/synthetics/docs/openapi/README.md

@@ -0,0 +1,8 @@
+# OpenAPI (Experimental)
+
+The current self-contained spec file is YAML and can be used for online tools like those found at <https://openapi.tools/>.
+This spec is experimental and may be incomplete or change later.
+
+A guide about the OpenApi specification can be found at [https://swagger.io/docs/specification/about/](https://swagger.io/docs/specification/about/).
+
+To join these files with the rest of the Kibana APIs, refer to `oas_docs/README.md`