Add Carbon (BuySellAds) ad provider for waiting room #6195

Job	Run time
build-and-check	3m 4s
test-integration-packages/internal	1m 3s
test-integration-packages/billing	1m 5s
test-integration-common	45s
test-integration-cli	55s
test-integration-sdk	1m 19s
test-integration-packages/agent-runtime	39s
test-cli	58s
test-.agents	44s
test-sdk	48s
test-common	50s
test-packages/billing	38s
test-integration-web	41s
test-packages/internal	49s
test-packages/agent-runtime	52s
test-web	52s
	16m 2s

Provide feedback