update oci l2 BGC file pattern, make netCDF version optional in the file ext format

[yufeizhu600]

When I test the PACE OCI L2 BGC reader, I have found the file extension of the data product files I have downloaded from NASA Earthdata is .nc instead .nc4 as the file pattern definition in the oci_l2_bgc reader.
This PR make the netCDF version in the file pattern optional in the config file to deal with this scenario.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.08%. Comparing base (fa56be5) to head (ad45b67). Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2996   +/-   ##
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  Coverage   96.08%   96.08%           
=======================================
  Files         377      377           
  Lines       55155    55155           
=======================================
  Hits        52997    52997           
  Misses       2158     2158           

Flag	Coverage Δ
behaviourtests	3.94% <ø> (ø)
unittests	96.18% <ø> (ø)

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[coveralls]

Pull Request Test Coverage Report for Build 11958130611

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.193%

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Totals
Change from base Build 11936881763:	0.0%
Covered Lines:	53241
Relevant Lines:	55348

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