pants ci: add integration tests jobs #5500

Job	Run time
Skip Duplicate Jobs Pre Job	3s
Self-check on Python 3.8 - Python 3.8	7m 40s
Unit Tests (chunk 1) - Python 3.8	3m 11s
Unit Tests (chunk 2) - Python 3.8	3m 11s
Lint Checks (black, flake8, etc.) - Python 3.8	2m 8s
Pack Tests - Python 3.8	2m 43s
Unit Tests (chunk 1) - Python 3.9	3m 3s
Compile (pip deps, pylint, etc.) - Python 3.8	3m 6s
Integration Tests (chunk 1) - Python 3.8	4m 55s
Unit Tests (chunk 2) - Python 3.9	3m 10s
Lint Checks (black, flake8, etc.) - Python 3.9	2m 10s
Integration Tests (chunk 2) - Python 3.8	4m 45s
Compile (pip deps, pylint, etc.) - Python 3.9	3m 31s
Pack Tests - Python 3.9	2m 46s
Integration Tests (chunk 1) - Python 3.9	5m 13s
Integration Tests (chunk 2) - Python 3.9	6m 3s
Slack notification for failed master builds	2s
	57m 40s

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