Ensure watchers are enabled before handling NGINX config context update

[dhurley]

Proposed changes

Ensure watchers are enabled before handling NGINX config context update.

Checklist

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

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.31%. Comparing base (fab01ec) to head (c33eab5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1464   +/-   ##
=======================================
  Coverage   85.31%   85.31%           
=======================================
  Files         102      102           
  Lines       12974    12974           
=======================================
  Hits        11069    11069           
  Misses       1418     1418           
  Partials      487      487           

Files with missing lines	Coverage Δ
internal/watcher/watcher_plugin.go	72.91% <100.00%> (ø)

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