Move git status updates to a background thread #2 (#24722)

Follow-up of https://github.com/zed-industries/zed/pull/24307

Brings back the PR and fixes the issue with the git status not
propagated, if computed too slow.
Now, git repo update
* waits in the background for all `scan_dir` repo status updates and
triggers another status update send afterwards
* ensures that the update sent is reported correctly (`scanning = true`)
if either FS or status scan is running still
* during worktree's git statuses updates, bumps `status_scan_id` to
ensure the repo update is reported to all subscribers

Release Notes:

- Improved project panel's speed in large projects

crates/collab/.env.toml

@@ -18,6 +18,7 @@ SEED_PATH = "crates/collab/seed.default.json"
 LLM_DATABASE_URL = "postgres://postgres@localhost/zed_llm"
 LLM_DATABASE_MAX_CONNECTIONS = 5
 LLM_API_SECRET = "llm-secret"
+OPENAI_API_KEY = "llm-secret"
 
 # SLACK_PANICS_WEBHOOK = ""