prefer AirbyteVersion over String

[cgardens]

What

• We have an abstraction called AirbyteVersion to make it easy to interact with versions and perform various operations on them. Throughout the codebase though, we tend pass the version around as a String. We need to lean into this abstraction. It gives us type safety guarantees. It also allows us to push noisy serialization issues out to the edge of our system. With the string, there were a lot of odd checks to make sure it was not empty and such deep in our internals.
• Going forward we should be pretty vigilant about passing AirbyteVersion instead of String.

How

• Search and destroy. Find String usages, replace with AirbyteVersion
• I skipped the airbyte-migrations submodule as that was going to be a real pain, and we plan to remove it soon anyway.