Use Mamba instead of Conda?

[AdrianDAlessandro]

There is a micromamba docker image that might be worth checking out for efficiency improvements.

[dandavies99]

Nice find and this cuts down the build time and final image size both by somewhere between 2x and 3x. It also means we are installing into the base environment, so don't need to mess around to use specific conda environment within Docker. See #16.

However, for reasons discussed in person, it might be best to stick with miniconda for this example to keep things consistent. I'll close that PR but leave this issue open to remind me to:

• Add a note to the docs that micromamba is an option, with links to the micromamba docker image.