TP: replace compass/ruby

[shamrickus]

This PR changes the TP sass compiler from compass (deprecated) to dart-sass (official sass compiler). As a result, ruby is no longer a dependency of TP.

It also changes the TP build docker file to always install nodejs 12.

---

Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Portal
• CDN in a Box

What is the best way to verify this PR?

Note: CiaB (and associated CI) for TP build will always fail (until merged) as it is using the dockerhub TP image, which was built using nodejs 10. gulp-dart-sass requires nodejs 12.

Build TP locally and confirm that it works.
Build TP using pkg with the -b command (so it uses the correct nodejs version).
Verify that TP looks correct.
Check the docs and make sure ruby/compass are no longer mentioned.

It is also possible to diff dist/resources/styles and see that the CSS is mostly the same with a few exceptions. First, sourceMaps are now specified by comments instead of through media queries. Second, the compass minification doesn't remove some chars that dart-sass does, as a result the new CSS should always be at least as small.

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[zrhoffman]

#6278's TP GHA failed due to #6283 needs to be rebased onto master now that #6284 is merged in order to pass

[ocket8888]

The grunt watch task still references "compass", which means that live-reloading (or what passes for it in AngularJS) is currently broken on this branch.

[ocket8888]

Changes look good, UI appears unchanged, RPMs build fine

As noted in the PR description, actions are expected to fail due to bad published images on Dockerhub. The changes in this PR include a fix for that, but they can't be updated until it's merged.

[zrhoffman]

Note: CiaB (and associated CI) for TP build will always fail (until merged) as it is using the dockerhub TP image, which was built using nodejs 10. gulp-dart-sass requires nodejs 12.

As noted in the PR description, actions are expected to fail due to bad published images on Dockerhub. The changes in this PR include a fix for that, but they can't be updated until it's merged.

Our build-rpms action checks for whether the GO_VERSION file was changed in the last commit (or in the PR, if it's being run on a PR), and, if so, builds the builder image instead of pulling it:

trafficcontrol/.github/actions/build-rpms/build-rpms.sh

Lines 33 to 35 in 1f56100

	if <<<"$files_changed" grep '^GO_VERSION$'; then
	pkg_command+=(-b)
	fi

So the action would pass if you added the TP builder Dockerfile to the list of files to check for, in addition to GO_VERSION (see #6210, which adds the TR builder Dockerfile).