Update docs for `ChannelDetails` fields which change on splice #21117

Job	Run time
ext-test	7m 48s
build (self-hosted, stable)	1h 18m 1s
build (windows-latest, stable)	2h 22m 23s
build (self-hosted, beta)	1h 39m 56s
build-tx-sync (macos-latest, stable)	7m 38s
build-tx-sync (ubuntu-latest, stable)	4m 47s
build (macos-latest, 1.75.0)	1h 37m 36s
build-tx-sync (ubuntu-latest, 1.75.0)	5m 33s
build (self-hosted, 1.75.0)	1h 50m 42s
build-tx-sync (macos-latest, 1.75.0)	7m 55s
build-tx-sync (ubuntu-latest, beta)	4m 38s
build (macos-latest, stable)	1h 36m 46s
linting	2m 19s
fuzz	1h 18m 11s
build-tx-sync (macos-latest, beta)	5m 7s
rustfmt	17s
benchmark	16m 40s
check_release	3m 1s
check_docs	3m 54s
coverage	44m 37s
	13h 37m 49s

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