Backend: Recognize .gitlab-ci.yaml for CI/CD pipeline

Workaround

Following this thread, users can navigate to Settings => Ci/cd in general pipeline, and set .gitlab-ci.yaml as a custom CI/CD file path

Summary

The CI/CD pipeline only recognizes the .yml extension for the .gitlab-ci file.

It should also recognize a .yaml extension since it as also a valid extension for a YAML file.

Steps to reproduce

• Add a valid .gitlab-ci.yaml file to a repository
• Observe that no CI/CD pipeline is detected
• Rename .gitlab-ci.yaml to .gitlab-ci.yml
• Observe that the CI/CD pipeline is now detected

What is the current bug behavior?

No CI/CD pipeline is created for a valid .gitlab-ci.yaml file

What is the expected correct behavior?

CI/CD pipeline should be created for .yaml file (same as if it were .yml)

In case that two files versions of the files exists in the repositorygitlab-ci.yaml and a gitlab-ci.yml, yml should always be the preceden

Output of checks

This happens on GitLab.com

Implementation table

1. Refactor usage of .gitlab-ci.yml as the default... (!134538 - merged)
2. Refactor frontend usage of .gitlab-ci.yml inline (!134887 - merged)
3. Use project CI config path to show CI blob viewer (!136549 - merged)
4. Fix checking the gitlab_ci_yml of a project (!141990 - merged)
5. Delete Project#uses_default_ci_config? (!142892 - merged)
6. Delete Repository#gitlab_ci_yml method (!149563 - merged)