graphql: Allow gunicorn logging config to be effective

Refs. swh/infra/sysadm-environment#5327

apps/swh-graphql/entrypoint.sh

@@ -7,9 +7,14 @@ case "$1" in
         exec bash -i
         ;;
     *)
+        EXTRA_CLI_FLAGS=""
+        if [ ! -z "${SWH_LOG_CONFIG_JSON}" ]; then
+            EXTRA_CLI_FLAGS="--log-config-json ${SWH_LOG_CONFIG_JSON}"
+        fi
         echo Starting the swh-graphql API server
         exec gunicorn --bind 0.0.0.0:${PORT} \
              --log-level ${SWH_LOG_LEVEL:-INFO} \
+             ${EXTRA_CLI_FLAGS} \
              --threads ${THREADS} \
              --workers ${WORKERS} \
              --timeout ${TIMEOUT} \

apps/swh-graphql/requirements.txt

@@ -6,3 +6,4 @@ h11
 starlette
 typing-extensions
 swh-graphql
+python-json-logger