docs: ensure edit links point to main branch

[12rambau]

Fix #1237

Proposal to solve the issue using solution 1.

• overwrite our template to add an extra method in the url parsing
• create a to_main method to digest the link and reroute it to main branch

[drammock]

If you didn't already do this @12rambau I think maybe we should check how other extensions do this? You'll see below my comment about hard-coding "main" that seems fragile; I'd like to think that there's a way to avoid that.

[drammock]

hmm, not working on the CI build: on this page https://pydata-sphinx-theme.readthedocs.io/en/stable/user_guide/index.html the "edit on GitHub" link goes here: https://github.com/pydata/pydata-sphinx-theme/edit/d7be3e599ef634820f0b1e049fc1f69e4707d05a/docs/user_guide/index.md (which is a 404). Is there reason to expect it to fail on CI builds but work in deployment?

[drammock]

argh, never mind, I clicked the wrong link on this page so I was viewing the current dev docs, not the PR docs. This looks to be working as expected.