Introduce Dummy Hop support for Blinded Payment Path #21107

Job	Run time
fuzz	1h 5m 51s
check_docs	3m 44s
linting	2m 21s
check_release	3m 11s
benchmark	17m 4s
rustfmt	16s
build-tx-sync (ubuntu-latest, 1.75.0)	5m 45s
build-tx-sync (ubuntu-latest, beta)	4m 44s
build-tx-sync (ubuntu-latest, stable)	4m 50s
build-tx-sync (macos-latest, beta)	8m 0s
build-tx-sync (macos-latest, stable)	8m 25s
build-tx-sync (macos-latest, 1.75.0)	7m 41s
build (self-hosted, 1.75.0)	1h 19m 59s
build (macos-latest, 1.75.0)	1h 44m 18s
build (self-hosted, beta)	2h 1m 44s
build (self-hosted, stable)	2h 1m 42s
build (windows-latest, stable)	2h 19m 44s
build (macos-latest, stable)	1h 44m 26s
ext-test	8m 8s
coverage	37m 4s
	14h 8m 57s

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