feat(project): add new endpoint

[agong-coveo]

Added this new endpoint

• This endpoint updates a project's resource associations without having to pass the whole project model;
• It allows us to add /remove specific resources to the precised projects.

NOTE: I've also tested this new endpoint with the current feature that I'm implementing.

Acceptance Criteria

• My changes are publicly available, documented, and deployed in production. (i.e. on Swagger)
• JSDoc annotates each property added in the exported interfaces
• The proposed changes are covered by unit tests
• Commits containing breaking changes a properly identified as such
• README.md is adjusted to reflect the proposed changes (if relevant)
• My merge commit message will be conventional (See Conventional Commit)