T5319: remove workarounds for defaults in high-availability.py

[jestabro]

Change Summary

Convert conf_mode script high-availability.py to use automatic defaults. This change is PR'd separately as it also resolves the problem in T5350 (Confusing warning message when committing VRRP config) and is the example mentioned in the discussion of defaults and invariants in

#2010

TLDR: the revision uses the option with_defaults to get_config_dict to merge only defaults of leaf nodes with a parent in the config; this avoids the spurious warning in T5350 and the need to manually trim garp settings if not set by user.

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):
  Update to avoid workarounds.

Related Task(s)

• https://vyos.dev/T5319
• https://vyos.dev/T5350

Component(s) name

vrrp

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