docs: add a "What's new in v2" page #3338

Job	Run time
checks / readme-snippets	14s
checks / docs	42s
checks / pre-commit	51s
checks / test (3.10, locked, windows-latest)	2m 12s
checks / test (3.13, locked, windows-latest)	1m 57s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 30s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 28s
checks / test (3.11, locked, ubuntu-latest)	1m 24s
checks / test (3.13, locked, ubuntu-latest)	1m 17s
checks / test (3.13, lowest-direct, windows-latest)	1m 49s
checks / test (3.10, lowest-direct, windows-latest)	1m 57s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.14, locked, windows-latest)	2m 42s
checks / test (3.10, locked, ubuntu-latest)	1m 15s
checks / test (3.14, lowest-direct, windows-latest)	1m 42s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 14s
checks / test (3.12, lowest-direct, windows-latest)	1m 53s
checks / test (3.12, locked, ubuntu-latest)	1m 42s
checks / test (3.12, locked, windows-latest)	1m 58s
checks / test (3.11, locked, windows-latest)	1m 58s
checks / test (3.11, lowest-direct, windows-latest)	1m 53s
checks / test (3.14, locked, ubuntu-latest)	2m 17s
all-green	5s
	36m 48s

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