[Synthetics] Space aware private locations !! (#202634)

## Summary

Fixes https://github.com/elastic/kibana/issues/199976

User can choose which space the location will be visible in while
creating a location !!


### Testing

- [ ] Create location in all spaces and make sure it's visible
everywhere.
- [ ] Creation location in a specific space and make sure it's only
visible in specified space


<img width="1728" alt="image"
src="https://github.com/user-attachments/assets/6aa5cac9-500a-447a-8ef5-bf53e91a16dd"
/>

docs/api/synthetics/private-locations/create-private-location.asciidoc

@@ -37,6 +37,9 @@ The request body should contain the following attributes:
 - `lat` (Required, number): The latitude of the location.
 - `lon` (Required, number): The longitude of the location.
 
+`spaces`::
+(Optional, array of strings) An array of space IDs where the private location is available. If not provided, the private location is available in all spaces.
+
 [[private-location-create-example]]
 ==== Example
 
@@ -53,6 +56,7 @@ POST /api/private_locations
     "lat": 40.7128,
     "lon": -74.0060
   }
+  "spaces": ["default"]
 }
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