NSFS | add configuration flag to enable dynamic supplemental groups allocation

[nadavMiz]

Explain the changes

1. add environment variable to enable/disable dynamic supplemental groups allocation
2. in case this value is set in the configuration file. the configuration file value will override the default value
3. change os_linux, os_darwing to get supplemental groups dinamicly only when this flag is not false

Issues:

GAP

implement and test on containerized environment: dynamic supplemental groups should work. need to test environment variable passes correctly to fs_worker

Testing Instructions:

1. automatic tests: sudo node ./node_modules/mocha/bin/mocha src/test/unit_tests/test_nsfs_access.js
2. manual tests:
   a. add new user with uid that matches an fs user with supplemental groups
   b. add new user that his GID matches a group user 1 is a part of
   c. create new bucket by user 2
   d. add "NSFS_ENABLE_DINAMIC_SUPPLEMENTAL_GROUPS" : false to config.json
   e. put object using user 1
   f. operation should fail. should get permission denied

• Doc added/updated
• Tests added