[#62106126] Implements jdbc_connection #metadata_for_dataset

 - Uses Sequel::Database#schema to get the schema info for a dataset, size is the number of columns
[#62106126] Implements jdbc_connection #datasets_count
Drop teradata fixtures when rebuilding fixtures to keep freshness.
Stub a JdbcConnection instance method in search controller spec because teradriver fails loudly in stdout.

Will see if there is a better solution when addressing search for jdbc data sources.