CI/CD: Refactor building docker images

[akihironitta]

What does this PR do?

• Fixes the current failures in nightly docker image builds.
• Unifies the following docker-related workflows into one workflow file:
  • docker build .github/workflows/ci-pytorch_dockers.yml
  • docker build & push .github/workflows/events-nightly.yml

Motivation

• This PR reduces the risk of pushing docker images with the wrong build arguments. For example, in master, there's a discrepancy between our CI and CD:
  https://github.com/Lightning-AI/lightning/blob/61c28cb428a13c2aea6d7f3f55e0f00431a4ea4e/.github/workflows/ci-pytorch_dockers.yml#L58-L59
  https://github.com/Lightning-AI/lightning/blob/61c28cb428a13c2aea6d7f3f55e0f00431a4ea4e/.github/workflows/events-nightly.yml#L70-L71

Does your PR introduce any breaking changes? If yes, please list them.

None

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PR review

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Did you have fun?

Make sure you had fun coding 🙃

cc @carmocca @akihironitta @Borda

[Borda]

let's rename it as ci-cd-pytorch_dockers.yml as it covers also releasing

[carmocca]

You might want to consider fixing the commit history and doing a rebase and merge to maintain the file's git history. Or renaming the file in a separate PR

LGTM either way!

[rohitgr7]

I'd say rebase and merge... if not too hard.