NC | Avoid concurrency master key manager initialization

[romayalon]

Explain the changes

1. manage_nsfs.js -

• account_management() - call nc_mkm.init() - in order to avoid concurrent calls master key manager initialization that might cause race conditions. call init() only if action is account add/update or show_secrets flag was provided (show_secrets can be passed in account list/status).
• list_config_files() - inside the loop - decrypt access keys only if show_secrets is set to true - reduce calls to nc_mkm.init() which will reduce calls for reading/getting the master keys json.

2. nc_master_key_manager.js - add prints for debugging.

Issues: Fixed #xxx / Gap #xxx

Testing Instructions:

• Doc added/updated
• Tests added