Create endpoint for obtaining and deleting all settings in Settings Sync API

The problem

VSCode Settings Sync has a feature to display all the synced data and to delete it from the cloud

See all synced data	Delete all data

GitLab's API compatible with VSCode settings sync should provide endpoints to enable this functionality.

Solution

Implement the following endpoints in the REST endpoints

• GET /resource/[resource_type] to fetch all the resources of a given type.
• DELETE /resource/[resource_type] to delete all the resources of a given type.

Availability and Testing

Ensure updated test coverage in unit/integration/feature tests.