docs: add a "What's new in v2" page #3335

Job	Run time
checks / readme-snippets	12s
checks / pre-commit	50s
checks / docs	44s
checks / test (3.13, locked, windows-latest)	2m 2s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 14s
checks / test (3.10, locked, windows-latest)	2m 1s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.14, locked, ubuntu-latest)	2m 23s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.10, locked, ubuntu-latest)	1m 22s
checks / test (3.11, lowest-direct, windows-latest)	1m 52s
checks / test (3.13, locked, ubuntu-latest)	1m 20s
checks / test (3.14, lowest-direct, windows-latest)	1m 45s
checks / test (3.12, lowest-direct, windows-latest)	1m 55s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 20s
checks / test (3.12, locked, ubuntu-latest)	1m 34s
checks / test (3.14, locked, windows-latest)	2m 55s
checks / test (3.11, locked, windows-latest)	1m 52s
checks / test (3.11, locked, ubuntu-latest)	1m 21s
checks / test (3.10, lowest-direct, windows-latest)	2m 5s
checks / test (3.12, locked, windows-latest)	1m 48s
checks / test (3.13, lowest-direct, windows-latest)	1m 51s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 34s
all-green	5s
	36m 53s

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