GitlabCI Support

[CelianR]

Is your enhancement related to a problem? Please describe.

YAML is used for GitlabCI, it would be nice to have support for these files such as go-to definitions, code lenses, linting etc.

This would be mainly useful to navigate through jobs that use extends nodes, which might reference jobs from other files.

Describe the solution you would like

Definitions

Go-to definitions of a job referenced within a extends / needs node, a !reference tag.
Handle include nodes to go to the referenced files.

Usages

A code-lens for each referenced job or rule can be displayed to show the usages.
A job may be referenced within extends or needs nodes and any object can be referenced within !reference tags.

Describe alternatives you have considered

Additional context