Add signup source to signup event #5979

Job	Run time
build-and-check	3m 0s
test-integration-packages/billing	1m 6s
test-integration-packages/internal	1m 19s
test-integration-web	48s
test-integration-common	51s
test-common	45s
test-.agents	43s
test-packages/internal	55s
test-packages/billing	41s
test-integration-sdk	1m 18s
test-cli	55s
test-sdk	52s
test-web	50s
test-integration-cli	44s
test-integration-packages/agent-runtime	50s
test-packages/agent-runtime	47s
	16m 24s

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