Add support for SIGTTIN and SIGTTOU signals to the dirty arbiter,
allowing dynamic scaling of dirty workers at runtime without restarting
gunicorn.
Changes:
- Add TTIN/TTOU to DirtyArbiter.SIGNALS
- Add num_workers instance variable for dynamic count
- Add _get_minimum_workers() to enforce app worker constraints
- Add signal handlers for TTIN (increase) and TTOU (decrease)
- Update manage_workers() to use dynamic count
- Add documentation for dynamic scaling
- Add unit tests for signal handling
- Add Docker integration tests
The minimum worker constraint ensures TTOU cannot reduce workers below
what apps require (e.g., if an app has workers=3, minimum is 3).
Closes#3489
2639215aa3