Docs: Update README and examples/

I think the README for this project could use some cleaning up/simplifying. I think it would be also helpful to copy Open Next's architecture diagram into the README so first time users can understand what they're getting from an infra perspective. Additionally I think we should focus more on OpenNext. This construct didn't start out on OpenNext, so I think some docs are older.

I'd also like to update the examples/ to be 1 CDK app with different stacks for each type of example. There is no need to have separate CDK apps for each example. This will simplify updating dependencies too. Using this issue to track work.