Migrate Google calendar example DAG to new design AIP-47

[chenglongyan]

related: #22447

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[potiuk]

@chenglongyan -> I have just solved a problem where "[source]" links were missing and there are two things to add to make it works. Once I merge #24386 you will get errors for those missing parts, but maybe you can add them now:

1. __init__.py should be added for all folders in path of "tests/system/...../example*.py" so that the packages created are not "implicit" namespace packages
2. System Tests <_api/tests/system/providers/google/../index> link needs to be added to index to avoid "missing index in TOC tree"

Not sure if you need to do it (not sure if you create any empty directory here), but I'd recommend to rebase on top of my change and fix all problems - I hope to have my change merged soon.

[potiuk]

I will merge it and fix in bulk.