Support for mamba 2.0

[danielhollas]

mamba v2.0 is a big release, in which mamba was completely decoupled from conda and its CLI is now based on micromamba (standalone C++ implementation). For more details see https://mamba.readthedocs.io/en/latest/developer_zone/changes-2.0.html

If we upgrade to this version in the docker stack, the most significant breaking change is the --prefix/-p option was renamed to --root-prefix/-r so we'll have to change the Dockerfiles accordingly as this is used in bunch of places. QeApp Dockerfile will need to be adapted as well. For now we should stick to 1.5.x versions (which I did in #455).