Delete existing empty dest folder before rename

[Tulsishah]

Description

• Renaming a directory into an existing empty directory in HNS was causing an error from GCS.
• To support this feature and maintain consistency with FLAT buckets, we manually delete the empty directory before performing the rename operation.

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - Added
3. Integration tests - Added and run with automation https://fusion2.corp.google.com/ci/kokoro/prod%3Agcsfuse%2Fgcp_ubuntu%2Fpresubmits%2Fperf_tests%2Fpresubmit/activity/da24a85e-e032-4361-a8d2-103ee3b7bc29
   Without the fix, the additional test was failing and I could see RenameFolder error from the logs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.28%. Comparing base (f2d240d) to head (4aa449a).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2568      +/-   ##
==========================================
+ Coverage   78.20%   78.28%   +0.08%     
==========================================
  Files         107      107              
  Lines       11802    11805       +3     
==========================================
+ Hits         9230     9242      +12     
+ Misses       2081     2071      -10     
- Partials      491      492       +1     

Flag	Coverage Δ
unittests	78.28% <100.00%> (+0.08%)	⬆️

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[ankitaluthra1]

minor comments, also could you please add integration test links in description Test section, the new test and an old test where rename fails if directory is not empty and rename passes when dest directory doesnt exist,

[Tulsishah]

minor comments, also could you please add integration test links in description Test section, the new test and an old test where rename fails if directory is not empty and rename passes when dest directory doesnt exist,

I've added it, and you can open it through the Kokoro button from the checks section. All the old tests are passing, and I've added a new test case where the destination directory exists and is empty. You can see the successful results from Kokoro in the passes results section.

[gargnitingoogle]

Oh I just noticed that this got merged in the middle of my review.