Edit on GitHub link is broken on our stable docs

[drammock]

On our dev docs it works: the link on this page goes here

On our the same page in our stable docs the link goes here which is a GitHub 404 page.

The difference in the links is that the dev docs link goes to github.com/.../edit/main/.../index.md while the stable docs goes to github.com/.../edit/<commit hash>/.../index.md.

I'm pretty sure the issue is that GitHub won't let someone propose changes to something other than the tip of a branch: if I go to a file on one of our very old branches I get an active "edit" button on GitHub. But since we don't habitually keep separate branches for our releases, the point in history associated with stable is not the tip of a branch, it's just a tag on main, so you get this:

Two solutions I can think of are:

1. always have the edit link go to main. If we delete or rename a file between stable and main it will still 404, but for most pages on stable the link will work
2. make a branch called stable and add it to our release process to do a squash-merge from main to stable once the release is cut. Then the edit links can all be github.com/.../edit/stable/... and should work.

I prefer option 1; if folks are proposing changes to our docs, most of the time we'll want those changes on main / in the dev version too, not just on stable, and if they're important changes we can cut a new patch release to update the stable docs right away too. Also I think we're not likely to delete or rename pages very often so the downside to option 1 seems minor.

Originally posted by @drammock in #1200 (comment)

[12rambau]

I'm +1 for option 1 as well