Add docs for ASGI Lifespan support #1287

Job	Run time
Run tests with different pydantic versions	3m 10s
Run tests (3.10)	1m 48s
Run tests (3.9)	1m 53s
Run tests (3.8)	1m 53s
Run linters (flake8)	1m 29s
Run tests with coverage	2m 45s
Run linters (pydocstyle)	1m 29s
Run tests (3.11)	1m 49s
Run tests (3.13)	1m 48s
Run tests (3.12)	1m 51s
Run linters (pylint)	1m 33s
Run linters (mypy)	1m 34s
	23m 2s

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