[C++] Add S3 support to fs::FileSystemFromUri

[asfimport]

FileSystemFromUri doesn't support S3. This would give almost immediate support for S3 in python/R.

Reporter: Francois Saint-Jacques / @fsaintjacques
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #6403

_{Note: This issue was originally created as ARROW-7761. Please see the migration documentation for further details.}

[asfimport]

Francois Saint-Jacques / @fsaintjacques:
Issue resolved by pull request 6403
#6403