Add Gemini Pro freebuff model (#566) #6308

Job	Run time
build-and-check	2m 46s
test-integration-packages/billing	1m 5s
test-integration-packages/internal	1m 14s
test-integration-common	41s
test-integration-cli	49s
test-integration-packages/agent-runtime	47s
test-integration-sdk	1m 15s
test-integration-web	42s
test-packages/agent-runtime	39s
test-packages/internal	50s
test-packages/billing	39s
test-.agents	43s
test-web	1m 9s
test-common	50s
test-cli	1m 0s
test-sdk	43s
	15m 52s

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