build(docs): improve Makefile for docs

[agilgur5]

Summary

Used the docs Makefile in #2326 and made some improvements while working on it

Modifications

• the docker build can be extracted into a separate make command and re-used

• volumes need to be mounted in order to make changes to local dir and reflect in container (and vice-versa)

Notes to Reviewers

I actually still had trouble getting changes to reflect in the local dir properly. Moved to local usage of hugo and didn't debug further, but thought this was still a worthwhile improvement.

Future Work

• May want to update versions in the Dockerfile (e.g. to Go 1.21+), newer version of Hugo, etc
• $(COMMON_DOCKER_BUILD_ARGS) is no longer necessary as it's in a single place. But args for -v ... and -t ... could be consolidated if one wanted to do so (nbd either way imo)

[lucix-aws]

We have internal CI that consumes this makefile, we're not generally in a position to accept changes to it without risk of breakage.

[agilgur5]

without risk of breakage.

This isn't a breaking change though?

We have internal CI that consumes this makefile

The container variant also doesn't work locally, so I am guessing that your internal CI isn't using it either

we're not generally in a position to accept changes to it

That's totally your prerogative, but I would ask that you make that explicit to all potential contributors, instead of saying so after someone has already spent their time on a contribution. The CONTRIBUTING.md does not mention that nor does the Makefile itself, say, in a comment at the top.

There is also just no contributing guidelines for the docs what-so-ever, which made contributing a docs fix a good bit more difficult as a result as well