Using empty stateStartApiSuccess to indicate success

https://github.com/indeedeng/iwf/blob/6d54278aa6f242d7b77bf5a2a0ed1e3b31525507/service/interpreter/workflowImpl.go#L752

99.99% of the time, the value is true and we have to pass `"stateStartApiSuccess":true` to worker. We could make the field default as true so that we don't have to send this value.

However, a bool field default to true may be a bit confusing, so we could rename it to `stateWaitUntilFailed` in the IDL.
SDK can be adapted to the value

(old) -> (new)
start -> waitUntil
decide -> execute

Start with service/interpreter/workflowImpl.go at the referenced line, then review merged pull request #568 to understand the work already completed. Trace the IDL and SDK surfaces for stateStartApiSuccess and the start/decide mappings; done means the selected API behavior is consistent across those surfaces and covered by the repository's relevant tests.

Written by the indexing model from the issue text.