feat: add support for signed resumable upload URLs

[williambrode]

Fixes #289.

[williambrode]

I'm sure my code is not production-worthy yet but I wanted to create the PR to help show what the problem is from my debugging.

[williambrode]

I signed the CLA.

[williambrode]

This doesn't handle v2 signed urls because they use a different query param ("Signature" I believe). But I'm not sure that's a good reason to not support V4 signed urls. We can add this but I don't have a test for it.

[tseaver]

@williambrode Thanks for the patch!

Can you double-check that the e-mail you used to create the commit (Author: <wil*****de​@activision.com>) matches the email(s) associated with your signed CLA?

[williambrode]

@tseaver You are right my e-mail was wrong in the commit. I've fixed it.

[tseaver]

This change looks reasonable, given the bug report, but we need to add unit tests to cover the new cases ("x-goog-signature" in parsed_query / ``"X-Goog-sSgnature" in parsed_query`).

[WildSunLove]

@williambrode just wanted to follow up with you; are you able to write unit tests for this or would you like some support from us on that aspect. I know our testing framework might be a bit of a learning curve if this is your first external contribution :)

[williambrode]

Ah, I didn't quite realize that was directed at me. I can take a look at adding the test.

[WildSunLove]

Haha, reading over Tres' message again, it might not have been, I think I was hasty in my pass-through.
We can definitely handle getting a unit test written unless you'd like to give that a shot.

[WildSunLove]

Alright, gave a go at the unit test. How's that look @tseaver ?

[cojenco]

Updated the unit tests to cover signed url uploads. @tseaver PTAL, thanks!