Metadata Functions for SchemaSpy

I was trying to run SchemaSpy on a DuckDB database with indices defined, and it was dying after throwing a host of exceptions related to missing metadata functions. I took a [stab at implementing the ones it was complaining about](https://github.com/joshuashaffer/duckdb-java-schema-spy-metadata/commit/b416a2ef19df61b5dae9500ecde94c3430fc3ee7), and it seems to work now by producing diagrams. (There are still a few left, but they seem recoverable.)

I'm not a JDBC expert, so I don't know if this is good enough. Is this good enough for a PR, or what else would you like to see?