Support DROP SCHEMA statements

[scsmithr]

Is your feature request related to a problem or challenge?

We're able to create schemas with datafusion, but can't drop them. I'm mostly concerned about doing cleanup in sqllogictests that create schemas (e.g. #6022). Without a way to drop, we might end up with name conflicts.

Describe the solution you'd like

Support DROP SCHEMA <schema> [CASCADE]

Describe alternatives you've considered

Again, I'm mostly concerned about sqllogictests. The alternative being we just ensure every test case uses a unique schema name if it needs a schema.

Additional context

No response

[jaylmiller]

I've tackled this in PR #6096 😀