DEV - Simplify Docker images

[trallard]

This is a stack on top of #838

Description

This PR continues to simplify the development and test setup for conda-store

• Removes unnecessary environment.yaml files (less files to keep in check/updated)
• Simplifies and adds comments to Dockerfiles
• Bumps the base image to [24.3.0-0](https://hub.docker.com/layers/condaforge/mambaforge/24.3.0-0/images/sha256-21f7908a6c984ae164cb51c8af71ef9901693630f4b744038e5df6ef968d9b05?context=explore)

Pull request checklist

• Did you test this change locally?
• Did you update the documentation (if required)?
• Did you add/update relevant tests for this change (if required)?

Additional information

Since this stacks on another PR, some integration and unit tests might fail (and will be fixed in #838). For now, the important parts are :

• Docker-related workflows, which are working.
• Integration tests (conda-store and conda-store-server) - in the sense that the container should be building and docker compose up should be working (which it is)

I built the Docker images locally, then used these ones for docker-compose, and all seemed to work.

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[peytondmurray]

A few comments, but on the whole this looks like a great simplification. I'm glad you spotted those test files unnecessarily getting copied in, too.

[peytondmurray]

Thanks for clearing up the questions I had 🚢