Write manifest file updates to a temp file first

[dhurley]

Proposed changes

Write manifest file updates to a temp file first, then validate that the temp file contains validate JSON before replacing the current manifest file with the temp one.

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

❌ Patch coverage is 47.36842% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.21%. Comparing base (c162d76) to head (f90fb9b).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/file/file_operator.go	47.36%	7 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1442      +/-   ##
==========================================
+ Coverage   85.18%   85.21%   +0.02%     
==========================================
  Files         102      102              
  Lines       12974    12984      +10     
==========================================
+ Hits        11052    11064      +12     
+ Misses       1437     1431       -6     
- Partials      485      489       +4     

Files with missing lines	Coverage Δ
internal/file/file_operator.go	60.83% <47.36%> (-2.81%)	⬇️

... and 6 files with indirect coverage changes

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