Add a py.typed file for submodule

[crwilcox]

To be in accordance with PEP 561 we should add a py.typed file to google/cloud/storage/py.typed

The file can be empty but does need to be present for some type checkers.

[crwilcox]

Do note, you may need to run mypy, pyright, pytype against our samples before merging. It will ensure that we aren't exposing users to failing type checks.

Ideally we would add this to CI as well, to avoid future breakage.

[cojenco]

Thanks @crwilcox for bringing this to our attention. We're planning to add the py.typed files after we finish deprecating Python 2 these coming weeks. Wanted to check if this is blocking anyone or any urgency for doing this sooner?

[crwilcox]

This shouldn't be blocking anyone. Feel free to schedule it for then.

[alex-statsig]

This was removed due to #734 a month after, and its been two years now; is there any plan to re-open / re-add this?

[rmorshea]

see #393