Add hugo version check and theme update to Makefile

[nginx-jack]

Proposed changes

This should help prevent any hugo or hugo-theme version drift going forward, and warn when versions are out of date.

• Add hugo version check and theme update to Makefile
• Update README.md with correct make target behaviors
• Add hugo-entrypoint to allow extra commands when docker starts
• Update hugo theme version in go.mod
• Use slimmer hugo docker image

Closes #2544

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

[nginx-bot]

Hi @nginx-jack!

Thanks for opening this pull request!
Be sure to check out our Contributing Guidelines while you wait for someone on the team to review this.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.62%. Comparing base (1294e2d) to head (a6204fe).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2608   +/-   ##
=======================================
  Coverage   88.62%   88.62%           
=======================================
  Files         105      105           
  Lines        8116     8116           
  Branches       50       50           
=======================================
  Hits         7193     7193           
  Misses        866      866           
  Partials       57       57           

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

[kate-osborn]

Confirmed it works locally without hugo installed. Thanks @nginx-jack!