fv3net environment on apple chips

[brianhenn]

Adds conda fv3net environment installation for Apple chips (M1, etc), since gfortran (a dependency of fv3net) is available for this architecture now. Also clarifies the conda-lock process by removing some extraneous commands and files.

Note: doesn't currently install due to #2266 .

Requirement changes:

• Pins conda-lock to a version before its API changed to avoid confusion
• Ran make lock_deps/lock_pip following these instructions

Resolves #2256.

Coverage reports (updated automatically):

[brianhenn]

The version of conda-lock we use (0.4.1) was not actually reading this

[brianhenn]

The render command and the output it produced (the multi-platform conda-lock.yml file) was not actually used in making our environments.

[brianhenn]

Requires that we use a version of conda-lock that uses the conda-lock -f environment.yml -p <platform> command to make platform-specific lock files.

Alternatively, we could switch to using a version >=1.0, in which we'd need to use a different conda-lock command (conda render or conda-lock --kind explicit) to implement that approach we've used. See docs.