gitserver: enable sg maintenance by default
Created by: stefanhengl
"sg maintenance" is running on Cloud since Dec 16, 2021 without issues. We saw a 4x speed-up for git-log operations for deeply nested folders in very large repositories.
With this change "sg maintenance" is enabled by default and at the same time we disable the legacy janitor job "garbage collect". Customers can revert this change by settting "ENABLE_GC_AUTO" to "true" and "SRC_ENABLE_SG_MAINTENANCE" to "false".