Add environment-to-ini to docker image (#14762)

* Add environment-to-app.ini routine

* Call environment-to-ini in docker setup scripts

* Automatically convert section vars to lower case to match documentation

* Remove git patch instructions

* Add env variable documentation to Install Docker

docker/rootless/usr/local/bin/docker-setup.sh

@@ -46,3 +46,6 @@ if [ ! -f ${GITEA_APP_INI} ]; then
     SECRET_KEY=${SECRET_KEY:-""} \
     envsubst < /etc/templates/app.ini > ${GITEA_APP_INI}
 fi
+
+# Replace app.ini settings with env variables in the form GITEA__SECTION_NAME__KEY_NAME
+environment-to-ini --config ${GITEA_APP_INI}