Adjust Settings Sync REST API to meet Settings Sync client expectations

Problem statement

In !131900 (merged), we delivered the initial implementation of the Settings Sync REST API for the Web IDE. This API satisfies most of the expectations of the VSCode Settings Sync client, however, we need to make some adjustments in the API responses.

Solution

• /manifest returns 204 No content when resources do not exist.
• /resource/[resource-type] allows fetching a list of saved resources of a given type.
• /resource/latest returns 204 no content when no resources exist.
• /resource/machines behave like any other resources with one exception: A single machine exists at the same time.
• POST endpoints return 200 code when succeeding
• Resource schema should contain the following fields:
  • version
  • machine id

Availability and Testing

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