Remove omnibus from docker-compose

What does this MR do?

Swaps out the omnibus nightly used in our docker compose file for a redis and postgres image. (And drops nginx).

The compose file is meant to allow us to test/debug/develop the images outside of the helm environment. (So we can easily identify the images are working, separate from our helm config)

Using omnibus nightly was slow, and we don't really need nginx for this to validate our images. I'm hoping to make use of the docker-compose environment in some ci-tests for our dsop release builds, so this is one of the clean-up items I have grabbed in order to get the environment ready.

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated