Nexus: Add Perlmutter to Nexus machines

[aannabe]

Proposed changes

The Perlmutter class was added to Nexus machines. It should be able to handle both CPU and GPU jobs depending on the requested node type via the constraint keyword. The job style was adapted from:
https://docs.nersc.gov/systems/perlmutter/running-jobs/

Also, I removed the Edison class since it was retired more than 3 years ago:
https://www.nersc.gov/news-publications/nersc-news/nersc-center-news/2019/edison-supercomputer-to-retire-after-five-years-of-service/

What type(s) of changes does this code introduce?

• New feature

Does this introduce a breaking change?

• No

What systems has this change been tested on?

• Perlmutter

Checklist

• Yes. This PR is up to date with current the current state of 'develop'

[jtkrogel]

@aannabe thanks for adding this. Please update the tests in nexus/tests/unit/test_machines.py to include the output from nxs-test -R machines --job_ref_table that corresponds to Perlmutter (and also check that it looks sensible).

[aannabe]

Edited the test_machines.py to account for Perlmutter and Edison changes. All the nxs-test tests are passing for me now.

[ye-luo]

Test this please