Do away with the requirement of adding every flag in mount_gcsfuse

[kislaykishore]

• Get the list of flags from the code-generated list and use that to automatically convert the persistent mount flags to appropriate format.

Description

Link to the issue in case of a bug fix.

https://b.corp.google.com/issues/368503898

Testing details

1. Manual - NA
2. Unit tests - Tested with existing unit tests.
3. Integration tests - NA

[codecov]

Codecov Report

Attention: Patch coverage is 50.40000% with 62 lines in your changes missing coverage. Please review.

Project coverage is 78.84%. Comparing base (a738c2a) to head (60810da).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
cfg/config.go	51.23%	13 Missing and 46 partials ⚠️
cmd/root.go	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2478      +/-   ##
==========================================
- Coverage   78.88%   78.84%   -0.05%     
==========================================
  Files         106      106              
  Lines       11686    11690       +4     
==========================================
- Hits         9219     9217       -2     
- Misses       1989     1993       +4     
- Partials      478      480       +2     

Flag	Coverage Δ
unittests	78.84% <50.40%> (-0.05%)	⬇️

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