Add Parcels versioning/deprecation policies and maintainer docs #85

Job	Run time
py3.12 \| macos \| integration tests	14m 50s
mypy	3m 44s
py3.12 \| ubuntu \| integration tests	18m 5s
py3.12 \| macos \| unit tests	8m 33s
py3.12 \| windows \| integration tests	18m 0s
py3.12 \| ubuntu \| unit tests	12m 54s
py3.12 \| windows \| unit tests	18m 0s
py3.10 \| ubuntu \| unit tests	12m 0s
py3.11 \| ubuntu \| unit tests	12m 6s
merge-test-artifacts	1s
	1h 58m 13s

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