Update Lightning Lite examples

[awaelchli]

What does this PR do?

Updates the examples to use the new CLI (no run method used). See #15506

Lightning Lite is also evolving to be more than just an onboarding tool for Trainer. The focus of the example has shifted away of teaching how to convert to a Lightning module and instead just focuses on showing how to integrate it with your existing PyTorch code.

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Did you have fun?

I made sure I had fun coding 🙃

cc @Borda @carmocca @justusschock @awaelchli

[carmocca]

Some of the examples were used in CI, you'll need to update that too

[awaelchli]

@carmocca Almost resolved. Just a tiny issue with the imports on the Lite GPU CI job.