Decouple database dependency from GRDBQueryKey

[acosmicflamingo]

If developers are to rely on the GRDB example as a guide for GRDB integration, it may be better to actually decouple the database dependency from GRDBQueryKey. Although everything currently works as-is because everything falls under the same namespace, I am finding that I can't simply copy and paste GRDBQueryKey code into my ComposableArchitectureExtensions library because the initializer has a database dependency that would be more appropriate to have in a separate library (e.g. LocalDatabaseClient).

I also think this is the way to go because I read somewhere in the Slack channel that the way Point-Free will be supporting GRDB isn't through some official code in the swift-sharing library itself, but rather an example that users can then copy-and-paste (which means it would be on us to maintain it after the code has made its way to our own codebases).

[mbrandonw]

Hey @acosmicflamingo, thanks for bringing this up! It is true that we don't want to currently support a full-fledged GRDB shared key for the library, but we can make the code in GRDBQueryKey.swift a little more self-contained. I have opened a PR (#15) for a slightly different approach, and so I will close this one for now.