[unsupported-object-issue-fix part1] Prep for fix empty directory list issue

[gargnitingoogle]

Description

This adds utility for ignoring GCS objects which aren't supported in GCSFuse mounts. These objects have // in their names or have names starting with /. These can't be represented in linux FS, hence need to be ignored in GCSFuse mount.

This is followed up in #1876 (implementation) and e2e tests (#2011) .

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - NA
3. Integration tests - NA

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.37%. Comparing base (3b6804a) to head (60257eb).
Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/util/gcs_util.go	92.30%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2561      +/-   ##
==========================================
- Coverage   78.38%   78.37%   -0.02%     
==========================================
  Files         107      108       +1     
  Lines       11793    11819      +26     
==========================================
+ Hits         9244     9263      +19     
- Misses       2058     2068      +10     
+ Partials      491      488       -3     

Flag	Coverage Δ
unittests	78.37% <92.30%> (-0.02%)	⬇️

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