UI can unintentionally add or remove project members

[jvstme]

Steps to reproduce

1. Open project settings in two tabs (simulate two admins editing the project simultaneously).
2. In the first tab, add User A to the project.
3. In the seconds tab, add User B to the project.

Actual behaviour

Only User B remains in the project. User A is unintentionally removed by the second tab.

Expected behaviour

Both User A and User B remain in the project.

dstack version

0.19.40

Solution

• In the UI, switch from /api/projects/{project_name}/set_members to /api/projects/{project_name}/add_members and /api/projects/{project_name}/remove_members.
• Deprecate /api/projects/{project_name}/set_members.