jdbc: metadata: provide info re database limits

[DatabaseMetaData][1].

Methods:

* getMaxColumnsInGroupBy
* getMaxColumnsInIndex
* getMaxColumnsInOrderBy
* getMaxColumnsInSelect
* getMaxColumnsInTable
* getMaxConnections
* getMaxLogicalLobSize
* getMaxRowSize
* getMaxStatements
* getMaxTablesInSelect
* doesMaxRowSizeIncludeBlobs

[1]: https://docs.oracle.com/javase/8/docs/api/java/sql/DatabaseMetaData.html