Endpoint to update service accounts as a group owner

What does this MR do and why?

This merge request adds functionality to update service account users in top-level groups. It introduces a new API endpoint to modify service account details like name and username. The changes include updates to the API documentation, implementation of the update service, and corresponding policy adjustments to control who can perform these updates. Additionally, the code includes new tests to ensure the proper functioning of this feature and handles various edge cases and error scenarios. The update capability is restricted to group owners with appropriate checks for feature licensing and user permissions.

References

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• Fixes #514528 (closed)

MR acceptance checklist

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Setup SaaS simulation in gdk
2. Create a group with ultimate license
3. create group service account

curl --request POST \
  --url https://gdk.test:3000/api/v4/groups/<group_id>/service_accounts \
  --header 'PRIVATE-TOKEN: <PAT>' \
  --header 'content-type: application/json' \
  --data '{
  "name": "name",
  "username": "my username",
  "email": "email@example.com"
}

1. Use List endpoint to make sure that service account is created

curl --request GET \
  --url https://gdk.test:3000/api/v4/groups/<group_id>/service_accounts

1. Update service account from API

curl --request PUT \
  --url https://gdk.test:3000/api/v4/groups/<group_id>/service_accounts/<service_account_id> \
  --header 'PRIVATE-TOKEN: <PAT>' \
  --header 'content-type: application/json' \
  --data '{
  "name": "new name"
}