ref: Migrate from rusoto to aws-sdk-s3

[Swatinem]

Supercedes #849, CC @josb

Merges the latest changes from master, cleans up the error handling and adds back support for custom regions.

Fixes #575

[codecov-commenter]

Codecov Report

Base: 65.95% // Head: 66.05% // Increases project coverage by +0.09% 🎉

Coverage data is based on head (d2743fa) compared to base (ac4e0a9).
Patch coverage: 45.50% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #954      +/-   ##
==========================================
+ Coverage   65.95%   66.05%   +0.09%     
==========================================
  Files          74       74              
  Lines       11754    11759       +5     
==========================================
+ Hits         7752     7767      +15     
+ Misses       4002     3992      -10     

Impacted Files	Coverage Δ
.../symbolicator-service/src/services/download/gcs.rs	41.29% <0.00%> (ø)
...mbolicator-service/src/services/download/sentry.rs	18.40% <0.00%> (ø)
.../symbolicator-service/src/services/download/mod.rs	74.79% <33.33%> (ø)
...s/symbolicator-service/src/services/download/s3.rs	42.89% <37.69%> (+5.58%)	⬆️
crates/symbolicator-sources/src/sources/s3.rs	89.75% <71.42%> (-5.63%)	⬇️
...symbolicator-service/src/services/download/http.rs	82.53% <100.00%> (ø)

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[josb]

Thanks for pulling this across the finish line, @Swatinem! I was just about to push my own updates to deal with the latest SDK, which included similar changes to the error handling. I hadn't gotten quite as far cleaning it up and handling all the necessary cases as needed but I was getting there, albeit slowly, and enjoying the learning process. Since the SDK isn't yet GA I figured there was still time to finish this PR, because it would have been nice to complete this myself. But I understand and appreciate your work to land this.

[Swatinem]

I should have communicated the intent here better.

We have already done a few refactors to all the downloader related things, and next up on that list would be to change the main downloader interface, in particular replacing DownloadError. That would probably have caused a lot of pain keeping up to date, so to avoid that, I wanted to land this prior to that next big step.

[josb]

No worries, @Swatinem. Had I known I would have pushed my changes for the latest AWS SDK sooner, because I spent several hours trying to understand and address the error handling changes. And I was on my way to clean them up, but granted it would have taken me way more time than you. ☺ I had planned to address the endpoint issue, too; I would have figured it out eventually but it would have taken me a while, due to my lack of experience and time to devote to this project. Given the refactoring you describe, merging this soon does seem like the right approach.