Add pg_stat_statments to hush-house cloudsql terraform.

[YoussB]

Background:

• In order to be able to get query statistics, we need to have the pg_stat_statments extension enabled on Google Cloud SQL.
• @zoetian and I were able to accomplish that by running the SQL statement: CREATE EXTENSION pg_stat_statements.
• The idea behind this issue is to be able to either automate that in our database terraform, or at least document it somewhere so we can run it when recreating the environment.