NSFS | NC | nsfs service additions

[romayalon]

Explain the changes

1. Added needed env vars to nsfs service
2. Added a check when creating fs_napi for GPFS lib file existence before reading the lib file - and added this check boolean in use_gpfs_lib().

Issues: Fixed #xxx / Gap #xxx

1. https://issues.redhat.com/browse/MCGI-201

Testing Instructions:

1. Run NC nsfs with the GPFS path as env variable while lib file exists
2. Run NC nsfs with the GPFS path as env variable while lib file does not exist
3. Run NC nsfs without the GPFS path as env variable

• Doc added/updated
• Tests added

[romayalon]

@tangledbytes I added a default nsfs_env.env file as an example that should be linked to /etc/noobaa.conf.d/.env
and added it as an environmentFile to be used in nsfs.service, please re-check it