docs: update SwaggerUI version

[agilgur5]

Follow-up to #10923, where the version of Swagger UI added there was already a year+ old at the time of the PR

Motivation

• use latest 5.11.0 instead of the 2 years outdated 4.5.0

  • it seems like the version was taken directly from the SwaggerUI installation docs, which still has an old version listed
    • EDIT: I sent a PR upstream to update it: docs: update unpkg installation to use latest version swagger-api/swagger-ui#9489
    • in fact, the entire code block was taken from the doc
      • fix invalid inline HTML in this code block (see below)

• this seems to make it slightly more performant, which is our main issue, but also has other benefits of using a current version of a dep

Modifications

• update the SwaggerUI dep loaded in a script tag on the docs site's Swagger page

• significantly simplify the HTML code block as it renders inside of existing MD/HTML

  • a second DOCTYPE, html, head, body, etc tags are actually invalid HTML, but either mkdocs ignored some of those or browsers just ignore some of those
    • fixing invalid HTML makes this doc page more robust
  • also fix the indentation in the code block too, which also did not meet style guidelines

• add a markdownlint-disable comment to allow the inline HTML

  • add a comment describing why it's necessary
    • similarly add a comment to the PR template explaining why that one is necessary too
  • remove the Makefile's ignore on swagger.md for docs linting et al

Verification

1. make docs still passes
   • including docs-lint, docs-spellcheck, etc
2. open site/swagger/index.html renders fine

[terrytangyuan]

this seems to make it slightly more performant, which is our main issue

What performance issue?

[agilgur5]

What performance issue?

Try opening any API method in the Swagger UI and watch it lag, freeze, or straight up crash the browser window.

It's a very prominent issue and was even mentioned in #10923, the original PR that added this (as linked at the top of the description). JM briefly mentioned it on Slack too and I agreed there that it is very hard to use in its current state due to the lag etc.
There's also some historical issues on the performance of the Swagger UI within the Server's UI as well: #6645 (this PR is for the docs, but same issues as they both have the same giant Swagger file and use Swagger UI)

As I wrote, this seems to make it better, but does not fix it. Anecdotally, it didn't crash on me once I made the update and it froze the whole page less often - i.e. it mainly lagged, which is the least bad UX effect of the 3 performance issues seen.
It likely needs more performance related fixes upstream, but those will only come in v5+ regardless

[isubasinghe]

Nice work, this actually makes the UI a lot more usable.

[agilgur5]

Fixed merge conflict

[agilgur5]

Gonna merge this in as it has already been approved and is a nice perf boost for the docs. I also already upgraded the UI to v5 in #12540, which required a more careful process.

[agilgur5]

Backported this update into release-3.5 in f4470ed. Will probably do the same for release-3.4