Replace miniconda with micromamba in the Docker image

[AdeelH]

Overview

This PR replaces miniconda with micromamba in the Docker image. See the links below for some discussion of why mamba is better than conda.

• https://pythonspeed.com/articles/faster-conda-install/
• https://blog.hpc.qmul.ac.uk/mamba.html

Checklist

• Added needs-backport label if PR is bug fix that applies to previous minor release
• Ran scripts/format_code and committed any changes
• Documentation updated if needed
• PR has a name that won't get you publicly shamed for vagueness

Notes

N/A

Testing Instructions

• Check if image builds correctly.

[codecov]

Codecov Report

Merging #1870 (002e51c) into master (81b74a8) will decrease coverage by 0.02%.
Report is 2 commits behind head on master.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1870      +/-   ##
==========================================
- Coverage   81.62%   81.61%   -0.02%     
==========================================
  Files         190      190              
  Lines        9278     9278              
==========================================
- Hits         7573     7572       -1     
- Misses       1705     1706       +1     

see 1 file with indirect coverage changes