Add unreferenced file integration tests

[spencerugbo]

Proposed changes

Add unreferenced file support to the mock management plane and add integration tests for it.

When sending a config apply request through the mock, the mock looks at the request body to identify unreferenced files. Here is a sample request body of a config apply that contains an unreferenced file:

   {
        "unreferencedFiles": [
            {
                "file_meta": {
                    "name": "/opt/homebrew/etc/nginx/test/unreferenced.conf",
                    "permissions": "0644"
                }
            }
        ]
    }

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 86.43%. Comparing base (012b734) to head (ace57ea).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1399      +/-   ##
==========================================
+ Coverage   86.28%   86.43%   +0.14%     
==========================================
  Files         102      102              
  Lines       12572    12603      +31     
==========================================
+ Hits        10848    10893      +45     
+ Misses       1248     1232      -16     
- Partials      476      478       +2     

see 13 files with indirect coverage changes

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