Update project documentation and remove legacy redirects
When most of the documentation in this project was moved to https://gitlab.com/gitlab-org/release/docs, we left stubs redirecting there.
A lot of these documents don't even apply anymore (ce-to-ee-merge anyone?) and are just added noise.
I've also added some basic "bootstrap" documentation for adding and running tests. The plan is to expand on this in the future with documentation aimed at developers contributing to and maintaining release-tools, such as best practices with Retriable, gotchas with ReleaseTools::Project classes, and so on.
6777fa2c - Update Variables documentation
79dceb86 - Simplify the ChatOps documentation
This document was grossly outdated as of gitlab-com/chatops!49 (merged).
I've opted to reduce the scope of what we document, since most of the
commands are self-documenting via --help.
The new aim is to give examples of the more common "entry" tasks, which then usually contain additional ChatOps command that the user is just copy-pasting.