Fix some CI wording in documentation
What does this MR do?
- Adds definitions page to CI docs.
- Adds image of pipelines list (although currently missing border that is on other images).
- Changes CI to CI/CD in
/doc
and/doc/ci
- Sorts user documentation in
/doc
Are there points in the code the reviewer needs to double check?
I'm not sure how to generate the border on the screenshot for pipelines. Pipelines is now mentioned in CI documentation, but it's still not mentioned from the doc root, so anyone who is confused by the new Pipelines tab still won't know where to look. I considered calling the link "CI/CD Pipelines", but stopped short.
Why was this MR needed?
Because grammar and confusion.
What are the relevant issue numbers?
Partially fixes #17733 (closed).
Screenshots (if relevant)
[Edit] Pulled grammar tweaks out to separate MR.