#763: CMIP6Plus plugin update to add HadGEM3 MM and UKESM1.0

[matthew-mizielinski]

Updates the CMIP6Plus model plugins with HadGEM3-GC31-MM and UKESM1-0-LL and copies the model config file over from CMIP6.

[mo-laurenboon]

Tests pass and ruff is happy with these files. However, I have noticed there isn't a ruff.toml on this branch and run_all_tests doesn't appear to be applying a linter. Running a ruff check on the entire branch is flagging some blank line/trailing whitespace issues. Should this be placed into a separate issue?

[matthew-mizielinski]

Tests pass and ruff is happy with these files. However, I have noticed there isn't a ruff.toml on this branch and run_all_tests doesn't appear to be applying a linter. Running a ruff check on the entire branch is flagging some blank line/trailing whitespace issues. Should this be placed into a separate issue?

This is branched from v3.3_release rather than main, i.e. before ruff was introduced. I'll ensure that all tests pass after the cherry-pick to main