Error and exit on validator configs that contain only `LOW` validators #6198

Job	Run time
rust-check-git-rev-deps	20s
fmt	21s
cargo-deny (advisories)	46s
build (gcc, current)	37m 56s
cargo-deny (bans licenses sources)	44s
build (gcc, current, --check-test-tx-meta)	18m 53s
build (gcc, next)	38m 5s
build (gcc, next, --check-test-tx-meta)	17m 12s
build (clang, current)	22m 49s
build (clang, current, --check-test-tx-meta)	14m 54s
build (clang, next)	23m 33s
build (clang, next, --check-test-tx-meta)	16m 11s
complete	1s
	3h 11m 45s

Provide feedback