Document equivalent/similar functionality for Postgres extensions

[chriscasano]

Chris Casano (chriscasano) commented:

On a regular frequency customers ask which Postgres extensions are supported in CockroachDB. Today create extensions is a no-op, but for customers migrating from Postgres their app may depend on functionality from these extensions. Postgis is an obvious one that we support now in 20.2. But there are others where similar functionality can be found with the uuid-ossp extension and the UUID data type for CockroachDB. ps_stat_statements comes up to and most of the metrics are already in our statements page. It would be good to have a docs page that outlines this so customers can figure out what they adopt or where they may have a loss of functionality.

Here are Postgres extension that comes with the Postgres source code: https://www.postgresql.org/docs/9.5/contrib.html and there's more out in the wild: https://www.postgresql.org/download/products/6-postgresql-extensions/

Jira Issue: DOC-825