Add tribal knowledge base and /executorch-kb skill (#19003) #2900

Job	Run time
test-coreml / test-backend-macos (coreml, operators) / macos-job	15m 31s
test-coreml / test-backend-macos (coreml, models) / macos-job	17m 27s
test-coreml / package-golden-artifacts	0s
test-coreml / test-backend-linux	0s
	32m 58s

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