[3006.x] Add coverage contexts to show what tests touch which files

[MKLeb]

What does this PR do?

Adds contexts to our coverage html reports. This will allow us to see which files touched what lines.

NOTE: We want to publish the json reports for this to GH Actions artifact storage, as they are the best format to parse out the contexts.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• [ ] Docs
• [ ] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [x] Tests written/updated

Commits signed with GPG?

Yes

[s0undt3ch]

FYI, just pushed a commit to this PR