chore: Replace markup_txt with rfc2html

[larseggert]

This is a subset of #6629 that leaves the reStructured text stuff alone.

[rjsparks]

This is a pretty major change, not just a library substitution for similar effect.

It essentially pulls a differently stylized htmlized view onto the main document page, replacing the plaintext view, getting use to even more confusion about where people should look.

We need to push for less, and that's a bigger conversation than what we should have in a PR.

[larseggert]

So I would be all in favor of completely removing the preview from this template, and force people to click the button for the rendering they want.

[larseggert]

Should I remove the preview?

[rjsparks]

We need to push for less, and that's a bigger conversation than what we should have in a PR.

I think we should have this discussion with the community (and really, this should be fodder for a more comprehensive UX-expert driven rework of the document display pages). Perhaps we should bring this up on tuesday's tools call.

[rjsparks]

To inform conversation Tuesday:

[rjsparks]

Based on the 12Dec tools call discussion, we should try to push this forward, but it's failing several tests.

[rjsparks]

It's now down to template validation failures - rfc2html may need tweaking?

[larseggert]

I have some validation ignores queued up for next week.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (02e0d96) 88.80% compared to head (584d5f1) 88.81%.
Report is 26 commits behind head on main.

Files	Patch %	Lines
ietf/doc/views_draft.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6632      +/-   ##
==========================================
+ Coverage   88.80%   88.81%   +0.01%     
==========================================
  Files         285      284       -1     
  Lines       40374    40361      -13     
==========================================
- Hits        35853    35846       -7     
+ Misses       4521     4515       -6     

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[rjsparks]

drafts for ads is still failing validation

[larseggert]

Hm. It passed after rebasing.

[jennifer-richards]

@larseggert - the cross-reference URLs generated by this were broken. At /doc/draft-ietf-stir-certificates-ocsp/#page-11 (for example), the link for [RFC5280] is https://dt-main.dev.ietf.org/doc/draft-ietf-stir-certificates-ocsp/rfc5280 rather than https://dt-main.dev.ietf.org/doc/rfc5280

This will be reverted by #6909. Because we squash-merged this, you should be able to rebase this branch onto main after the revert PR is merged.

[jennifer-richards]

I rebased the merged branch here: https://github.com/jennifer-richards/datatracker/tree/chore-remove-markup-txt-light

(You probably should double-check that I did that correctly as there were a few conflicts. Note that it does not include commits that did not leave any changes, so the commit count doesn't match this PR's 14 commits.)