Upgrade to postgres 15 in CircleCI

[tmpayton]

Summary

What we're after:
Production has been upgraded to Postgres version 15. On circleci, cms app is currently tested against postgres:13. Its time to update the circleci docker image to Postgres version 15.

Related issues

Completion criteria

• The circleci docker image is upgraded to postgres 15.
• Developers have been informed that CMS production database is now on 15 (Developers may still want to stay on 13 to continue to run API locally).

Tech steps or considerations (optional)

• update postgres image in circle/config.yml file
• npm/pytest run OK on circleci
• cms app deploys OK on circleci
• Let developers know that CMS production database is on 15, but that they may still want to stay on 13 to continue to run API locally.

[tmpayton]

For reference, upgrading to pg v15 causes this error message to appear in circleci: LOG: 42501: could not change directory to "/home/circleci/project": Permission denied. It can safely be ignored according to this GitHub ticket.