Add 0.2 changelog (and quick missing spliec doc) #20867

Job	Run time
coverage	18m 11s
ext-test	6m 43s
build (self-hosted, 1.75.0)	52m 47s
build (self-hosted, beta)	2h 4m 49s
build (self-hosted, stable)	1h 40m 10s
build (macos-latest, stable)	1h 47m 53s
build (windows-latest, stable)	2h 20m 28s
build (macos-latest, 1.75.0)	57m 49s
build-tx-sync (ubuntu-latest, stable)	4m 56s
build-tx-sync (macos-latest, stable)	7m 49s
build-tx-sync (ubuntu-latest, 1.75.0)	5m 24s
build-tx-sync (macos-latest, 1.75.0)	7m 50s
benchmark	16m 23s
build-tx-sync (macos-latest, beta)	7m 20s
build-tx-sync (ubuntu-latest, beta)	4m 39s
check_release	3m 8s
rustfmt	16s
check_docs	5m 13s
linting	2m 34s
fuzz	56m 18s
	12h 10m 40s

Provide feedback