Add a .run_command() method to Runners

[AdeelH]

Overview

This PR adds a .run_command() method to all Runners. The main motivation is to make it easy to run the predict and predict_scene commands remotely.

Checklist

• Added needs-backport label if PR is bug fix that applies to previous minor release
• Ran scripts/format_code and committed any changes
• Documentation updated if needed
• PR has a name that won't get you publicly shamed for vagueness

Notes

N/A

Testing Instructions

N/A

[codecov]

Codecov Report

Merging #1981 (8aa44e2) into master (ad4743e) will decrease coverage by 0.11%.
The diff coverage is 22.50%.

❗ Current head 8aa44e2 differs from pull request most recent head 0f0ca43. Consider uploading reports for the commit 0f0ca43 to get more accurate results

@@            Coverage Diff             @@
##           master    #1981      +/-   ##
==========================================
- Coverage   86.22%   86.11%   -0.11%     
==========================================
  Files         195      193       -2     
  Lines        9567     9513      -54     
==========================================
- Hits         8249     8192      -57     
- Misses       1318     1321       +3     

Files	Coverage Δ
...ision_aws_batch/rastervision/aws_batch/__init__.py	100.00% <ø> (ø)
...e/rastervision/pipeline/runner/inprocess_runner.py	100.00% <100.00%> (ø)
...eline/rastervision/pipeline/runner/local_runner.py	98.36% <100.00%> (+0.05%)	⬆️
...on_pipeline/rastervision/pipeline/runner/runner.py	83.33% <ø> (ø)
...rastervision/aws_sagemaker/aws_sagemaker_runner.py	75.32% <15.38%> (-12.18%)	⬇️
...s_batch/rastervision/aws_batch/aws_batch_runner.py	55.73% <9.09%> (+2.61%)	⬆️

... and 4 files with indirect coverage changes