global config option to set default "Custom CI config path"
### Description
I'm working on getting CI/CD working well on the new, official Debian gitlab: https://salsa.debian.org. Its pretty close to working quite well, but there is one small detail: the default location for _.gitlab-ci.yml_ does not work for the vast majority of Debian's almost 50,000 packages. Most packages in Debian are "non-native" packages, e.g. the source is not maintained in Debian, only the packaging parts. The git repos for non-native packages only allow modifications in the _debian/_ sub-directory. Anything in the root directory is considered part of the original, upstream source for the package.
Switching the "Custom CI config path" preference to _debian/.gitlab-ci.yml_ works fine, so this should be the default for Debian's gitlab. As far as I can tell, there is no way to set this default right now.
### Proposal
Add global config option so that the gitlab admin can set the default for "Custom CI config path" to something besides _.gitlab-ci.yml_ in the root of the project.
### Links / references
https://salsa.debian.org/salsa/support/issues/26
issue