blob/s3blob: support URL query parameters to override aws.Config fields

[vangent]

Fixes #1357.

[codecov]

Codecov Report

Merging #1359 into master will decrease coverage by 0.03%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1359      +/-   ##
==========================================
- Coverage   76.28%   76.25%   -0.04%     
==========================================
  Files          57       57              
  Lines        4390     4418      +28     
==========================================
+ Hits         3349     3369      +20     
- Misses        882      890       +8     
  Partials      159      159

Impacted Files	Coverage Δ
aws/aws.go	0% <0%> (ø)	⬆️
blob/s3blob/s3blob.go	86.68% <73.33%> (-0.57%)	⬇️

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[zombiezen]

Hey Robert! I agree with adding the region parameter, but I'm not as onboard with other changes in this PR. I'd like to decouple a few (I realize you were on a time crunch), but I think we can wait to get this right. Stepping through:

[vangent]

PTAL

[vangent]

I can also update this to set SharedConfigEnable, LMK.

[vangent]

Gentle ping @zombiezen ...

[zombiezen]

Decided offline: we'll make the SharedConfigEnable in a separate PR. We should also change the *Session that's in the default provider sets. @vangent, can you file an issue for that?

[vangent]

Decided offline: we'll make the SharedConfigEnable in a separate PR. We should also change the *Session that's in the default provider sets. @vangent, can you file an issue for that?

Done:
#1416