Lightning Lite docs

[awaelchli]

What does this PR do?

Part of #9987
This should be merged after #10175

This is the V1 for the new Lightning Lite package. Planned to be released as part of 1.5.

Demo

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Did you have fun?

I made sure I had fun coding 🙃

Part of #1 (it's a lie, this is just here to avoid noisy GitHub bot)

[tchaton]

Looks great !

[akihironitta]

This is cool 🔥

[rohitgr7]

so cool 🎉 🚀

[kaushikb11]

LGTM!