fix(fastapi): use metrics in cases where PROMETHEUS_MULTIPROC_DIR is defined

Previously, we restricted this to gunicorn to get it working on aur-dev.
This change makes it usable through any backend, and also no-op if
PROMETHEUS_MULTIPROC_DIR is not defined.

Signed-off-by: Kevin Morris <kevr@0cost.org>

docker/scripts/run-pytests.sh

@@ -22,6 +22,9 @@ while [ $# -ne 0 ]; do
     esac
 done
 
+rm -rf $PROMETHEUS_MULTIPROC_DIR
+mkdir -p $PROMETHEUS_MULTIPROC_DIR
+
 # Initialize the new database; ignore errors.
 python -m aurweb.initdb 2>/dev/null || \
     (echo "Error: aurweb.initdb failed; already initialized?" && /bin/true)