sdk: implement addAgentStep #4006

Job	Run time
build-and-check	2m 25s
test-integration-common	34s
test-integration-.agents	34s
test-integration-backend	29s
test-integration-web	34s
test-integration-cli	32s
test-integration-npm-app	33s
test-integration-packages/agent-runtime	31s
test-backend	34s
test-.agents	31s
test-packages/agent-runtime	42s
test-npm-app	42s
test-web	31s
test-cli	32s
test-common	39s
	10m 23s

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