Upgrade Production Database

[kkrug]

The PostgreSQL databases for Dev and Staging were already upgraded to version 15 per the request form Cloud.gov (see #1486 )
Before upgrading the production database, Elixir/Erlang/Phoenix must be upgraded in Staging and Production to be in sync with the Dev branch. This will allow us to apply the same SSL configuration found in the Dev version of prod.exs (i.e. verifying the certificate) to both Staging and Production.