feat: templating for brief and Actions text

[rich-iannone]

This PR adds the ability to use templating variables for strings passed to the brief= argument, available in all validation methods. If using a string as a value when calling Actions, that string could use an expanded set of templating variables (six in total). Documentation has been added to explain which vars can be used for brief= and within Actions.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.01%. Comparing base (27396fb) to head (2f7aad6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #78   +/-   ##
=======================================
  Coverage   99.00%   99.01%           
=======================================
  Files          16       16           
  Lines        3208     3240   +32     
=======================================
+ Hits         3176     3208   +32     
  Misses         32       32           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.