pants ci: add integration tests jobs (#6273) #5577

Job	Run time
Skip Duplicate Jobs Pre Job	4s
Self-check on Python 3.8 - Python 3.8	8m 50s
Pack Tests - Python 3.8	2m 41s
Unit Tests (chunk 1) - Python 3.8	12m 50s
Integration Tests (chunk 1) - Python 3.8	7m 50s
Lint Checks (black, flake8, etc.) - Python 3.8	2m 36s
Unit Tests (chunk 2) - Python 3.8	9m 53s
Integration Tests (chunk 2) - Python 3.8	7m 41s
Compile (pip deps, pylint, etc.) - Python 3.8	3m 57s
Unit Tests (chunk 1) - Python 3.9	12m 57s
Pack Tests - Python 3.9	2m 58s
Lint Checks (black, flake8, etc.) - Python 3.9	2m 53s
Unit Tests (chunk 2) - Python 3.9	9m 31s
Integration Tests (chunk 1) - Python 3.9	7m 1s
Compile (pip deps, pylint, etc.) - Python 3.9	3m 56s
Integration Tests (chunk 2) - Python 3.9	7m 1s
Slack notification for failed master builds	3s
	1h 42m 42s

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