feat: Use bs5 for htmlized doc

[larseggert]

This gets rid of a bunch of old code by re-using document_main to render htmlized docs into a new set of bs5-based templates.

Also fixes #4057 and #3653.

This depends on ietf-tools/rfc2html#11 and ietf-tools/rfc2html#12.

[rjsparks]

This is a pretty big change of what's really the most heavily fetched format from the datatracker. We may want to phase this in? (and possible fix the html brokenness in rfc2html at the same time).

As mentioned out of band, when I first moved this to the datatracker, I didn't preserve the colored header and got immediate feedback that people wanted it back.

Please look at #3466.

[larseggert]

I'm adding the colored header - as a colored badge.

[larseggert]

We may want to phase this in?

We should definitely deploy on sandbox first and ask for feedback.

[larseggert]

@rjsparks should we chat about how to make this available for community feedback?

[rjsparks]

We can do a deployment of the branch on the sandbox server using a new DNS name (such as htmlize-preview.ietf.org), or you could look at rewiring the PR to put this htmlization at a different endpoint than the current, so that they are both available in production for some time (/doc/htmlpreview/ perhaps). If we go with deploying the branch, it would be good to keep it close to main.

[larseggert]

I'll look I to adding another button for deployment testing via main.

Actually, it will require a lot of work to rework the PR for that. I think deploying the branch is easier. We can also first get some initial feedback during the codesprint.

[larseggert]

@rjsparks I think this is ready for you to take a look (htmlization and pdfization of various documents). If you think it's ready, maybe we do public testing?

[rjsparks]

Moving this into a branch at ietf-tools to assist with a feedback deployment