PyTorch Lightning Updates

[amogkam]

Various updates for PyTorch Lightning + Ray

• Fixes the PTL+Tune tutorial code highlighting. Closes Issue on page /tune/tutorials/tune-pytorch-lightning.html #17687.
• Upgrades PTL version to 1.4
• Adds Ray Lightning as an additional library and tests in CI
• Removes legacy lightning accelerators
• Deprecates Ray SGD LightningOperator

Why are these changes needed?

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[krfricke]

Can you fix the conflicts and lint? Happy to review afterwards

[amogkam]

Blocked on ray-project/ray_lightning#78

[amogkam]

OK this is ready for review again

[amogkam]

Hey can you guys take a look at this please

[richardliaw]

looks good, please merge when tests pass