config: T5330: add boolean check for additions by default in config dict

[jestabro]

Change Summary

For a config dict returned with defaults automatically merged (as in the case of get_interface_dict; get_accel_dict; or get_config_dict(..., with_defaults=True | with_recursive_defaults=True) ), it may be useful to know if an entry was set in CLI, or only merged with defaults: retain this information internally and add a configdict method from_defaults -> bool.

Simple example:

>>> conf = Config()
>>> base = ['interfaces', 'ethernet']
>>> # no defaults:
>>> d = conf.get_config_dict(base, get_first_key=True)
>>> pprint(d)
{'eth0': {'address': ['dhcp'],
          'description': 'test',
          'hw-id': '52:54:00:ad:9f:43',
          'ip': {'arp-cache-timeout': '40'}}}
>>> # merged defaults:
>>> _, d = get_interface_dict(conf, base, ifname='eth0')
>>> pprint(d)
{'address': ['dhcp'],
 'description': 'test',
 'dhcp_options': {'default_route_distance': '210'},
 'duplex': 'auto',
 'hw_id': '52:54:00:ad:9f:43',
 'ifname': 'eth0',
 'ip': {'arp_cache_timeout': '40'},
 'mtu': '1500',
 'speed': 'auto'}
>>> d.from_defaults(['mtu'])
True
>>> d.from_defaults(['dhcp_options'])
True
>>> d.from_defaults(['ip'])
False
>>> d.from_defaults(['ip', 'arp_cache_timeout'])
False

The method is present in the above cases get_interface_dict, get_accel_dict, get_config_dict(..., with_defaults=True | with_recursive_defaults=True).

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T5330

Component(s) name

Proposed changes

How to test

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[c-po]

Very cool, @zdc that's what you requested?