Docs: Add a Maintainer Guide / Maintenance section to the website

[JoshuaKGoldberg]

Before You File a Documentation Request Please Confirm You Have Done The Following...

• I have looked for existing open or closed documentation requests that match my proposal.
• I have read the FAQ and my problem is not listed.

Suggested Changes

Surfacing a discussion with @bradzacher: we really like how the ESlint website includes a maintainer guide at https://eslint.org/docs/latest/maintainer-guide. It's good form to document these things.

Going back through recent issues...

• Release cadence & strategies
• What constitutes a breaking change
• What to do for new TS versions
• What kinds of bug fixes & feature requests generally will or won't be accepted
• Philosophy of when we'll allow fixes and/or suggestions (e.g. Rule proposal: prefer-private-class-members  #5228)
• Edit: how to write an extension rule (e.g. the testing practice mentioned in feat(eslint-plugin): [no-shadow] add shadowed variable location to the error message #5183)

Affected URL(s)

typescript-eslint.io/docs/maintenance, perhaps?