Test failure summaries in CI

[neilmayhew]

Description

Add a small utility that extracts test failure info from log files and uploads them as JSON artifacts. Another utility in the same package then collates the failure artifacts at the end of the whole CI run and publishes a summary to the run web page. This reduces the need for a human to look at the log files, and provides the information necessary for reproducing failures locally (target, pattern and seed).

This summary could also be included in the Slack post from nightly failures, but it would be noisy and the summary is only a single click away anyway.

Checklist

• Commits in meaningful sequence and with useful messages.
• Tests added or updated when needed.
• CHANGELOG.md files updated for packages with externally visible changes.
  NOTE: New section is never added with the code changes. (See RELEASING.md).
• Versions updated in .cabal and CHANGELOG.md files when necessary, according to the
  versioning process.
• Version bounds in .cabal files updated when necessary.
  NOTE: If bounds change in a cabal file, that package itself must have a version increase. (See RELEASING.md).
• Code formatted (use scripts/fourmolize.sh).
• Cabal files formatted (use scripts/cabal-format.sh).
• CDDL files are up to date (use scripts/gen-cddl.sh)
• hie.yaml updated (use scripts/gen-hie.sh).
• Self-reviewed the diff.

[neilmayhew]

This is a draft for now because it contains a deliberate failure to show what the output looks like.

It can't be merged anyway with the failure in it, so I'll mark it ready for review.

[aniketd]

I think this is going to be super useful. Thanks @neilmayhew !