fix: Cleanup prometheus metrics for dead workers

The current "cleanup" function that is removing orphan prometheus files
is actually never invoked.
We move this to a default gunicorn config file to register our hook(s).

https://docs.gunicorn.org/en/stable/configure.html
https://docs.gunicorn.org/en/stable/settings.html#child-exit
Signed-off-by: moson <moson@archlinux.org>

aurweb/asgi.py

@@ -13,7 +13,6 @@ from fastapi import FastAPI, HTTPException, Request, Response
 from fastapi.responses import RedirectResponse
 from fastapi.staticfiles import StaticFiles
 from jinja2 import TemplateNotFound
-from prometheus_client import multiprocess
 from sqlalchemy import and_
 from starlette.exceptions import HTTPException as StarletteHTTPException
 from starlette.middleware.authentication import AuthenticationMiddleware
@@ -91,12 +90,6 @@ async def app_startup():
     get_engine()
 
 
-def child_exit(server, worker):  # pragma: no cover
-    """This function is required for gunicorn customization
-    of prometheus multiprocessing."""
-    multiprocess.mark_process_dead(worker.pid)
-
-
 async def internal_server_error(request: Request, exc: Exception) -> Response:
     """
     Catch all uncaught Exceptions thrown in a route.

gunicorn.conf.py

@@ -0,0 +1,7 @@
+from prometheus_client import multiprocess
+
+
+def child_exit(server, worker):  # pragma: no cover
+    """This function is required for gunicorn customization
+    of prometheus multiprocessing."""
+    multiprocess.mark_process_dead(worker.pid)