New API: signalOrStartWorkflow and invokeRpcOrStartWorkflow

**Context**
This will simplify a lot of the user code to catch exception on signal/invokeRPC and start workflow.

Temporal has "signalWithStart" as "signal if open, or start a new one with a signal -- this is too complicated.

What people usually need is “signal or start". This makes it easier to understand and use.

**How**
Two directions

Option 1, using Temporal's signalWithStart
Internally just send a garbage signal when starting to hack it.
But I am not sure how this would work for invokeRpcOrStart

Option 2, just call two Temporal APIs in service.go

Start by reviewing service.go and the existing Temporal signalWithStart and invokeRPC integrations. Clarify whether the new methods should use signalWithStart or separate Temporal APIs, and define the expected behavior for signalOrStartWorkflow and invokeRpcOrStartWorkflow before implementation.

Written by the indexing model from the issue text.