refactor: every project platform is also an account platform

Description

This MR refactors the GitLabPlatform that we use in common code.

Before this MR, we had distinct types for the project platform and the account platform. But in reality, the project platform is always an account platform. Without an account, there wouldn't be any project because to associate the git repository with the project we have to make API calls.

This MR prepares us for listening to account changes (critical for updating the Language Server config with a new token/account).

Related Issues

This MR is a continuation of !1162 (merged).

Matching MR in the WebIDE that adds the instance URL to the config: refactor: add gitlabUrl to interop config (gitlab-web-ide!260 - merged)

Part of LS: multiple accounts and self-managed support (#1054 - closed)

How has this been tested?

• Code suggestions work on desktop:
  • 
• Code suggestions work in WebIDE (for WebIDE testing process see the instructions on !1162 (merged))
  • 

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap