Migrate to go-viper blessed fork of mapstructure

[evankanderson]

Summary

See: https://github.com/go-viper/mapstructure/releases/tag/v1.6.0

There will be a v2 version, but it's currently in alpha.

Fixes #3148

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Unit tests

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 50.314% (-0.005%) from 50.319%
when pulling 34fdb44 on evankanderson:3148-migrate-from-mitchellhmapstructure-to-go-vipermapstructure
into 6c47102 on stacklok:main.

[evankanderson]

In particular, we need this workflow to pass: https://github.com/stacklok/minder-rules-and-profiles/blob/main/.github/workflows/lint.yaml

[evankanderson]

This is ready for another review; it turns out the go-viper fork is starting with a v2 with an API that's compatible with v1. /shrug