docker: rootless image (#10154)

* docker: rootless image

* improve docs + remove check for write perm on custom

* add more info on ssh passtrough

* Add comment for internal ssh server in container config

docker/rootless/etc/templates/app.ini

@@ -0,0 +1,58 @@
+APP_NAME = $APP_NAME
+RUN_USER = $RUN_USER
+RUN_MODE = $RUN_MODE
+
+[repository]
+ROOT = $GITEA_WORK_DIR/git/repositories
+
+[repository.local]
+LOCAL_COPY_PATH = $GITEA_TEMP/local-repo
+
+[repository.upload]
+TEMP_PATH = $GITEA_TEMP/uploads
+
+[server]
+APP_DATA_PATH = $GITEA_WORK_DIR
+SSH_DOMAIN       = $SSH_DOMAIN
+HTTP_PORT        = $HTTP_PORT
+ROOT_URL         = $ROOT_URL
+DISABLE_SSH      = $DISABLE_SSH
+; In rootless gitea container only internal ssh server is supported
+START_SSH_SERVER = true
+SSH_PORT         = $SSH_PORT
+SSH_LISTEN_PORT  = $SSH_LISTEN_PORT
+BUILTIN_SSH_SERVER_USER = $RUN_USER
+LFS_START_SERVER = $LFS_START_SERVER
+LFS_CONTENT_PATH = $GITEA_WORK_DIR/git/lfs
+
+[database]
+PATH = $GITEA_WORK_DIR/data/gitea.db
+DB_TYPE = $DB_TYPE
+HOST    = $DB_HOST
+NAME    = $DB_NAME
+USER    = $DB_USER
+PASSWD  = $DB_PASSWD
+
+[indexer]
+ISSUE_INDEXER_PATH = $GITEA_WORK_DIR/data/indexers/issues.bleve
+
+[session]
+PROVIDER_CONFIG = $GITEA_WORK_DIR/data/sessions
+
+[picture]
+AVATAR_UPLOAD_PATH = $GITEA_WORK_DIR/data/avatars
+REPOSITORY_AVATAR_UPLOAD_PATH = $GITEA_WORK_DIR/data/gitea/repo-avatars
+
+[attachment]
+PATH = $GITEA_WORK_DIR/data/attachments
+
+[log]
+ROOT_PATH = $GITEA_WORK_DIR/data/log
+
+[security]
+INSTALL_LOCK = $INSTALL_LOCK
+SECRET_KEY   = $SECRET_KEY
+
+[service]
+DISABLE_REGISTRATION = $DISABLE_REGISTRATION
+REQUIRE_SIGNIN_VIEW  = $REQUIRE_SIGNIN_VIEW