feat: add app status tracking to the backend (#17163)

This does ~95% of the backend work required to integrate the AI work.

Most left to integrate from the tasks branch is just frontend, which
will be a lot smaller I believe.

The real difference between this branch and that one is the abstraction
-- this now attaches statuses to apps, and returns the latest status
reported as part of a workspace.

This change enables us to have a similar UX to in the tasks branch, but
for agents other than Claude Code as well. Any app can report status
now.

coderd/database/migrations/000313_workspace_app_statuses.down.sql

@@ -0,0 +1,3 @@
+DROP TABLE workspace_app_statuses;
+
+DROP TYPE workspace_app_status_state;