Improve troubleshooting page with more tips and tricks

Problem to solve

Our troubleshooting guide at https://docs.gitlab.com/ee/ci/troubleshooting.html has some basic tips but we could expand this with more details around how to figure out what's going on when authoring/troubleshooting pipelines.

Further details

The page should include info on the linter, links to other docs areas with common troubleshooting sections (rules, for example). How to render a pipeline with includes, etc.

Proposal

Who can address the issue

Other links/references

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