Improve functional test notifications

🗣 Description

This changes how notifications by email work when functional tests fail. Instead of emailing the TCOs once per test plan failure, it now only emails once per product failure. Additionally, it adds a link directly to the GitHub workflow job, making it easier for TCOs to review the failures.

💭 Motivation and context

The first goal is to reduce email fatigue. The second goal is to make it easier for TCOs to find the problem.

Closes: #1365

🧪 Testing

Created a test workflow to identify how to create the URL and to send email only if one or more previous jobs failed. Transferred this knowledge to the functional test workflow.

✅ Pre-approval checklist

[x] This PR has an informative and human-readable title.
[x] PR targets the correct parent branch (e.g., main or release-name) for merge.
[x] Changes are limited to a single goal - eschew scope creep!

Almost. I fixed a long-standing error in omit_policies.yaml where it had the wrong EOL marker.

[x] Changes are sized such that they do not touch excessive number of files.
[x] These code changes follow the ScubaGear content style guide.
[x] Related issues these changes resolve are linked preferably via closing keywords.
[x] All relevant type-of-change labels added.
[x] All relevant project fields are set.
[x] All relevant functional tests passed.
[x] All automated checks (e.g., linting, static analysis, unit/smoke tests) passed.

✅ Pre-merge checklist

[x] PR passed smoke test check.
[x] Feature branch has been rebased against changes from parent branch, as needed
[x] Resolved all merge conflicts on branch
[x] Notified merge coordinator that PR is ready for merge via comment mention

✅ Post-merge checklist

[ ] Feature branch deleted after merge to clean up repository.
[ ] Verified that all checks pass on parent branch (e.g., main or release-name) after merge.

cisagov / ScubaGear