Use rasterio AWS session in RasterioSource when reading files on S3

[AdeelH]

Overview

This PR makes RasterioSource use rasterio's AWSSession when reading from a raster file on S3, which makes it easier to read from requester-pays buckets (e.g. NAIP).

Previously, the following (ipython) snippet would not work even if the user was logged into an SSO session via the AWS CLI; the user would need to export all the credentials to the environment to make it work. This PR fixes that.

%env AWS_REQUEST_PAYER=requester

from rastervision.core.data import RasterioSource

uri = 's3://naip-analytic/pa/2019/60cm/rgbir_cog/39075/m_3907515_nw_18_060_20191019.tif'
rs = RasterioSource(uri, allow_streaming=True)
chip = rs[:100, :100]

Checklist

• Added unit tests, if applicable
• Updated documentation, if applicable
• Added needs-backport label if the change should be back-ported to the previous release
• PR has a name that won't get you publicly shamed for vagueness

Notes

This PR also makes rastervision_aws_s3 recognize the AWS_REQUEST_PAYER environment variable and allow it to override Raster Vision's AWS_S3_REQUESTER_PAYS config option.

Testing Instructions

See new unit tests.

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.21%. Comparing base (a25fa34) to head (1b39b99).
Report is 39 commits behind head on master.

Files with missing lines	Patch %	Lines
...rvision/core/data/raster_source/rasterio_source.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2197      +/-   ##
==========================================
+ Coverage   90.15%   90.21%   +0.05%     
==========================================
  Files         198      198              
  Lines        9888     9902      +14     
==========================================
+ Hits         8915     8933      +18     
+ Misses        973      969       -4     

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