Adopt Docs Starter Pack config

[rkratky]

Fixes FR-5577.

This puts in place the same Read the Docs and Sphinx config as used by the https://github.com/canonical/sphinx-docs-starter-pack, which will make maintenance and upgrades easier.

[dbungert]

@rkratky - thanks for this!

I haven't reviewed the content too closely, just looking at CI as of yet, will look at content later.
The new test is failing, I'll let you consider what's going on there.

CLA check is also failing - https://github.com/canonical/subiquity/actions/runs/6422328325/job/17438594649?pr=1822#step:2:50 - I usually suggest using the @canonical email address, which should address this.

[rkratky]

Yeah. I forgot the CLA, but that's taken care of now. I'll need to look more closely at why the docs checks are failing.

[dbungert]

This looks mostly fine when the doccheck is fixed (I love the dead link checker), one question though.

[dbungert]

I presume library.canonical.com is not accessible to community contributors, is that correct?

[rkratky]

Goog point. I'll remove those.

[Chris-Peterson444]

This looks good! Thanks @rkratky

Also just one question from me.

[rkratky]

@dbungert Could you please approve now that the Subiquity checks have passed?

I'll need to work on the docs checks, but it will take a bit more time. Two of them are failing to run, so I need to find out why. The third one (linkcheck) is failing because of, well, invalid links -- so I'll submit another PR to fix them.

[dbungert]

I'll need to work on the docs checks, but it will take a bit more time. Two of them are failing to run, so I need to find out why. The third one (linkcheck) is failing because of, well, invalid links -- so I'll submit another PR to fix them.

I think the linkcheck links are failing on the manpages, can you confirm? We were purposefully using links that are redirecting to the latest series, does linkcheck not like those? Those links do work if I click them.