feat: Allow setting of the port number when using the --serve flag by adding a new --port (String) flag

[Riddhimaan-Senapati]

changes are in file osv-scanner/cmd/osv-scanner/internal/helper/helper.go

1.Added a global variable servePort with a default value of "8000"

2.Added a new CLI flag --port that allows users to customize the port number used when serving the HTML report

3.Removed the hardcoded port number from the ServeHTML function, using the global servePort variable instead

4. The flag's Action function updates the global servePort variable when a custom port is specified

These changes allow users to specify a custom port using the --port flag when using the --serve option, while maintaining the default port 8000 if no custom port is specified.

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[Riddhimaan-Senapati]

@jtt @abhisek @calebbrown @iurisilvio Can anyone of you review my PR? I have also just signed the Google CLA. Excited to begin contributing to this repository.

[hogo6002]

Hi @Riddhimaan-Senapati thanks for contributing! I like having a separate string flag to specify the port number instead of converting serve from a bool flag into a string flag.

Can you follow https://github.com/google/osv-scanner/pull/1557/checks?check_run_id=36491080803 and Github commit name convention to resolve failed tasks

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 69.30%. Comparing base (a5d0e2b) to head (cccacb7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/osv-scanner/internal/helper/helper.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1557      +/-   ##
==========================================
- Coverage   69.31%   69.30%   -0.02%     
==========================================
  Files         200      200              
  Lines       19038    19041       +3     
==========================================
  Hits        13196    13196              
- Misses       5135     5138       +3     
  Partials      707      707              

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[Riddhimaan-Senapati]

@hogo6002 Done, I have changed the PR title and fixed some linting issues in the code and created an appropriately named commit for that.

[another-rex]

LGTM, thank you!