[FEATURE]: Use mamba as a drop-in replacement of conda in readthedocs builds

[tomvothecoder]

Is your feature request related to a problem?

The repo's readthedocs build often times out with the message Build exited due to excessive memory consumption.

Example: https://readthedocs.org/projects/xcdat/builds/16450539/

I suspect this is related to conda (readthedocs/readthedocs.org#6412 (comment))

The main problem here is that conda consumes a lot of memory to do the package resolution. We had this problem in the past and it's a known issue in the conda community.

A possible solution is to use mamba as a drop-in replacement for conda to reduce memory consumption and decrease build time. https://docs.readthedocs.io/en/stable/guides/conda.html#making-builds-faster-with-mamba

Other fixes: https://docs.readthedocs.io/en/stable/guides/build-using-too-many-resources.html

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response