java/driver/flight-sql: implement current catalog/current schema via session options

[unikdahal]

Follow-up from #4444 review (comment by lidavidm).

The Go Flight SQL driver implements SetOption/current-catalog / current-schema by round-tripping through the session options API rather than being a local no-op:

arrow-adbc/go/adbc/driver/flightsql/flightsql_connection.go

Lines 149 to 162 in 60e010c

	// GetCurrentCatalog implements driverbase.CurrentNamespacer.
	func (c *connectionImpl) GetCurrentCatalog() (string, error) {
	options, err := c.getSessionOptions(context.Background())
	if err != nil {
	return "", err
	}
	if catalog, ok := options["catalog"]; ok {
	if val, ok := catalog.(string); ok {
	return val, nil
	}
	return "", c.Base().ErrorHelper.Errorf(adbc.StatusInternal, "server returned non-string catalog %#v", catalog)
	}
	return "", c.Base().ErrorHelper.Errorf(adbc.StatusNotFound, "current catalog not supported")
	}

The Java driver's FlightSqlConnection should do the same: back adbc.connection.catalog / adbc.connection.db_schema (current catalog / current schema) with the server-side session, matching Go's behavior, instead of leaving them unimplemented/local-only.