Refactor Dockerfile for conda

[klamann]

We should switch to micromamba for faster and smaller docker builds, and use mambaorg/micromamba as base image.

Also, maybe remove the need to use conda run before every command by modifying the default shell, see https://pythonspeed.com/articles/activate-conda-dockerfile

[carsten-bo]

We should not use the micromamba image as it doesn't support the complete conda api and doesn't come with the conda cli. It would deviate too much from the option cookiecutter option that is "conda".

Instead, we can go with the mamba base image and use mamba as it has faster package resolving. The image still also provides the conda cli in case it is needed and is therefore closer to our provided option.