chore: update viper

[cfabianski]

Description

Closes #1439

Updates Viper

Also:

• Make the binding public so that it can be tested
• Improve test coverage for env variables (particularly repository flags)
• Remove cycle dependency by splitting flag types.

In the end, the AutomaticEnv and the SetEnvPrefix wasn't the way to go because the values in EnvironmentVariables shouldn't used the prefixed version.
The current code is the final version which I believe is the simplest version.

Checklist

• I've added test coverage that shows my fix or feature works as expected.
• I've updated or added documentation if required.
• I've included usage information in the description if CLI behavior was updated or added.
• PR title follows Conventional Commits format

[cfabianski]

This PR would be useful if we wanted to improve it spf13/viper#1719