Is your feature request related to a problem?
gitlab-ci.yml is now a big long file with different tasks, which is hard to read and understand.
Describe the solution you'd like
gitlab-ci.yml file has the option to include external yml files:
see: https://docs.gitlab.com/ee/ci/yaml/#include
Especially the local and remote includes are interesting.
Describe alternatives you've considered
not needed
Additional context
improve readability and interoperability between the formulas is also possible.
No need to duplicate code (dry)