Remove github.com/samber/lo dependency from main application

What does this MR do?

• Remove github.com/samber/lo dependency from main application:

  For the Kubernetes changes, I've made it clearer that retry limits work on errors strings, not the error values.

  The provided errors only work by comparing with strings, and because errors.New("a") != errors.New("a"), to get around this, the custom error type used Is(err error) bool and strings.Contains. I think it's better to just directly surface that we're comparing error strings and not error values.

• Remove golang.org/x/exp/slices dependency.

Why was this MR needed?

• lo is not needed for the main application.
• golang.org/x/exp/slices is no longer needed because slices is now part of the Go stdlib.

What's the best way to test this MR?

Existing tests should work the same.

What are the relevant issue numbers?