[8th May 2024] Add deprecation notices to CodeQL for VS Code documentation

[subatoi]

On the 8th May, we're set to start automatically redirecting users from pages under https://codeql.github.com/docs/codeql-for-visual-studio-code/ to https://docs.github.com/en/code-security/codeql-for-vs-code/

This PR adds a deprecation note (reusable) to each of the pages under https://codeql.github.com/docs/codeql-for-visual-studio-code/, for those users whose browsers don't redirect. It also updates other instances of soon-to-be-outdated links in this repo, and adds a note to CONTRIBUTING.md about how to contribute to the newly migrated docs.

[mbg]

The changes in the go/ directory look fine.

[felicitymay]

Quite a few comments, but most are to link people to Installing CodeQL for Visual Studio Code - GitHub Docs when we tell them to set up the extension, rather than the generic article.

[tausbn]

Python changes LGTM. 👍

[felicitymay]

I made a couple of small fixes, but this looks ready to merge.

[subatoi]

@jf205 👋 Could you please have another look at this one? It looks like after you're OK with it, we should be set to merge tomorrow 😄

[subatoi]

Thanks @jf205 @felicitymay if one of you could kindly reapprove, I'll aim to have this merged in sync with the redirects tomorrow

[subatoi]

Just to note that @saritai will be keeping an eye out for the redirects PR to ship today, and then she'll merge this PR. The person merging the redirects PR is on Pacific Time and Sarita's on Eastern Time, so it will likely happen in the evening during British Summer Time.

cc @jf205