Better PostGIS support with Citus

PostGIS is a spatial database extender for PostgreSQL object-relational database. It adds support for geographic objects allowing location queries to be run in SQL.

Comes up very frequently in various prospect engagements. **PostGIS currently works with Citus** but just created this issue for re-evaluating/reviewing the specifics of what works and what doesn't, based on which coverage could be improved.

(The above is just a high-level summary of the issue, in future, this could be made elaborate with specific requirements).