Ignore plantuml images for test sites

[yucheng11122017]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:
  Resolves Testing sites with generated files #2498
  Also does Chore: Remove generated PUML image and exclude it from .gitignore #2497

Overview of changes:
Enable ignoring of plantuml images for test sites

Anything you'd like to highlight/discuss:
nil

Testing instructions:
nil

Proposed commit message: (wrap lines at 72 characters)
Enable ignoring of plantuml images for test sites

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

---

Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.14%. Comparing base (6cc2461) to head (c6bf4b3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2502   +/-   ##
=======================================
  Coverage   51.14%   51.14%           
=======================================
  Files         124      124           
  Lines        5359     5359           
  Branches     1152     1152           
=======================================
  Hits         2741     2741           
  Misses       2328     2328           
  Partials      290      290           

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[kaixin-hc]

lgtm! thanks for the quick fix

[github-actions]

@kaixin-hc Each PR must have a SEMVER impact label, please remember to label the PR properly.