Add GeoNetwork 2.8 to 2.10 postgis migration file and add missing 2.6 to 2.8 migration step to add a gt_pk_metadata table

Address review comments

Address review comments
Merge pull request #6 from aodn/add-missing-gt-pk-metadata-table

Add GeoNetwork 2.8 to 2.10 postgis migration file and add missing 2.6 to...