Revamp introductory CI/CD docs
Problem to solve
As part of &2072, including a lot of the comments there, as well in other issues discussions, it's clear we need to improve our introductory pages for this.
From &2072 (comment 372522592), we need to:
- Improve: https://docs.gitlab.com/ee/ci/quick_start/README.html, with a significant revamp.
- Set up an incremental list of examples that "build up" from simple to complicated, but making use of the most common features/keywords, linking out as needed.
- Raise it's visibility, perhaps by making it the main introduction page (and nesting the current intro below this, or combining them together).
- Discuss linking to a different CI/CD page from https://docs.gitlab.com/. Perhaps the getting started page or an improved introduction page. Right now we link straight to the YAML reference, and that might not be the best option.
Related to: #27071 (closed)
Edited by Marcel Amirault