ARROW-7761: [C++][Python] Support S3 URIs

[pitrou]

Allow instantiating an S3 filesystem instance from a s3://user:pass@bucket/path?params... URI.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-7761

[fsaintjacques]

Works great :D

01:build/ (pr/6403✗) $ time release/dataset-parquet-scan-example file:///home/fsaintjacques/datasets/nyc-tlc/parquet
Table size: 746
real 0m3.248s
user 0m5.832s
sys 0m0.203s
01:build/ (pr/6403✗) $ time release/dataset-parquet-scan-example 's3://123:12345678@nyc-tlc/parquet?scheme=http&endpoint_override=localhost:9000'
Table size: 746
real 0m5.600s
user 0m7.557s
sys 0m0.474s

[fsaintjacques]

One thing that I noted in my local integration, I had to explicit the global init of S3. I think it might be worth providing a default or implicitly calling the init step in FileSystemFromUri.

[pitrou]

@fsaintjacques Could you try again now?

[fsaintjacques]

I pushed a change to the dataset example, it seems to be lost did you push force before pulling? It was a small change, I can make it again.

[pitrou]

Oh, sorry. Yes, I force-pushed after rebasing :-/

[fsaintjacques]

It should pass the CI, I'll merge after. The diff of the dataset example shows how well designed the APIs is.