Pin docker image versions

What does this MR do and why?

Pins our dependent docker images to explicit version in docker-compose.yml.

This is due to relying on :latest being unpredictable since different people may get different dev environment depending on when they last docker-compose pulled.

A separate MR will add this repo to RenovateBot to make updating these pinned versions easier.

How to set up and validate locally

1. run the devkit
2. ensure all docker images match the versions specified (e.g. docker ps should show explicit versions are running instead of :latest)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Closes #32 (closed)