[#62106126] Implements :limit option for fetching jdbc datasets

 - jdbc#getTables does not seem to have any limit options, so we must fetch all
   the datasets and take from the result array
[#60860640] User can associate JDBC datasets with a workspace.

 - Also fixes an issue with the source tables filter on workspaces without a sandbox. If
   there was no sandbox, the source table filter would not include source tables due to
   constraint schema_id != sandbox_id (nil)