Add errors.Is support to the generated error types

[gwvandesteeg]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

Migrating code to the newer preferred system of checking for errors using errors.Is instead of a attempt to cast the error to a specific type identified that the errors generated by viper do not support this functionality.

Proposed Solution

Ensure errors.Is is supported by all error types and include tests for these to verify functionality.

For those errors that wrap other errors or are of a struct type we need to add the Is(err error) method.

This allows errors to be checked using both the old and new system.

Alternatives Considered

The alternative is the old way of handling errors.

Additional Information

No response

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