Add MessageIntrospector for message schema inspection #159

Job	Run time
build-and-test / build (24.X, jazzy)	9m 16s
build-and-test / build (24.X, humble)	6m 9s
build-and-test / build (24.X, rolling)	4m 14s
build-and-test / build (24.X, kilted)	7m 16s
	26m 55s

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