Add Carbon (BuySellAds) ad provider for waiting room (#529) #6221

Job	Run time
build-and-check	3m 23s
test-integration-packages/internal	1m 16s
test-integration-packages/billing	1m 15s
test-integration-cli	48s
test-integration-common	49s
test-integration-sdk	1m 24s
test-integration-packages/agent-runtime	45s
test-integration-web	47s
test-packages/agent-runtime	41s
test-packages/internal	45s
test-.agents	39s
test-packages/billing	46s
test-cli	57s
test-sdk	46s
test-web	1m 14s
test-common	43s
	16m 58s

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