Handle default value for azure addon policy

[viniciusdc]

Reference Issues or PRs

Previous ENH PR #2888 included a bug with the default variable value for the azure_addon_policy_enabled setting.

What does this implement/fix?

• Fixes the default value attr. for the recent addition while also including the missing field as a configurable option in the nebari-config.yaml schema.

Put a x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

• Did you test the pull request locally?
• Did you add new tests?

How to test this PR?

Any other comments?