Add setting to disable the sign in button (#30450)

Designed to pair with #30444 to enable enterprises to make it harder to
sign into the collab server and perhaps accidentally end up sending code
to Zed.

Release Notes:

- N/A

Co-authored-by: Mikayla Maki <mikayla@zed.dev>
96a0568fb7Tristan Hume committed on 5/14/2025, 1:39:04 PM· committed by GitHubparentb6828e5
3 files changedLine totals unavailable