Introduce Dummy Hop support for Blinded Payment Path #21182

Job	Run time
ext-test	5m 30s
build (windows-latest, stable)	2h 20m 15s
build (self-hosted, beta)	1h 17m 2s
build-tx-sync (macos-latest, 1.75.0)	8m 40s
build (macos-latest, 1.75.0)	1h 46m 42s
build-tx-sync (ubuntu-latest, 1.75.0)	5m 25s
build (self-hosted, stable)	1h 18m 8s
build (self-hosted, 1.75.0)	1h 19m 9s
build-tx-sync (macos-latest, beta)	8m 39s
fuzz	1h 6m 11s
build-tx-sync (ubuntu-latest, stable)	4m 48s
build-tx-sync (macos-latest, stable)	5m 6s
benchmark	16m 22s
build-tx-sync (ubuntu-latest, beta)	4m 56s
build (macos-latest, stable)	2h 7m 45s
rustfmt	17s
check_release	3m 11s
check_docs	5m 22s
linting	2m 24s
coverage	37m 47s
	13h 3m 39s

Provide feedback