Reorganize and create new CI Variables documentation
The current intro is too short and jumps right into a reference https://docs.gitlab.com/ee/ci/variables/
We need:
- a proper introduction and explanation of capabilities, use cases, benefits, concepts (and possibly to move the reference table to its own page)
- a tutorial doc to show an example use from A to Z (Marcia: I'm planning to give examples in-context; let's see if we need a dedicated tutorial after the MVC?)
- Consider whether to cover this item around docker-compose as part of this issue or to create a new one. (Marcia: prob out of the scope here. Will create another issue.)
Type of issue
Problem to solve
https://docs.gitlab.com/ee/ci/variables/ offers too little context, mainly a reference table
Further details
Per feedback from Mark P in this doc
Proposal
Who can address the issue
Other links/references
Edited by Marcia Ramos