Please include mamba/libmamba in your base and studiolab environment

**Is your feature request related to a problem? Please describe.**
Conda take as while to solve. Mamba/libmamba is faster and is recommended by Anaconda: https://www.anaconda.com/blog/a-faster-conda-for-a-growing-community. May you please add it to the base environment, so that we can spend more time actually using the GPU than waiting for conda to solve :) Either would be good: https://anaconda.org/conda-forge/mamba

**Describe the solution you'd like**
Add mamba to SageMaker Studio Lab base so that you can mamba install a new custom environment quickly

**Describe alternatives you've considered**

- installing Mamba first, then conda installing
- pip install
- Conda install

The issue names the SageMaker Studio Lab base and studiolab environments but no repository file or test. Start by locating how those environments are defined and how packages are provisioned, then check whether mamba or libmamba can be added safely. Done means a new environment can use the requested faster package solver.

Written by the indexing model from the issue text.