feat(workflow): Support workflow ID conflict policy

[antlai-temporal]

What was changed

Added workflowIdConflictPolicy to workflow start and SignalWithStart

Checklist

1. Closes #1392
2. How was this tested:

Added two integration tests

[antlai-temporal]

@dandavison Thanks a lot for a careful review of the docstrings, it made a huge difference!

[stephanos]

@antlai-temporal 👋 what's standing in the way of merging? Asking since this is the last PR before we can publish the documentation.

[antlai-temporal]

@antlai-temporal 👋 what's standing in the way of merging? Asking since this is the last PR before we can publish the documentation. Sorry @stephanos just saw your comment. I was waiting for @mjameswh to give me the go ahead, I don't think this will be controversial...

[mjameswh]

Sorry @stephanos and @antlai-temporal for the delay. I was on FTO.

It just so happens that I was reviewing this PR tonight, and I actually do have concerns that I want to resolve before this API reaches a TS release. Please hold on just a bit longer.

[stephanos]

@mjameswh no worries; I was actually informed that the docs are only blocked on the Go SDK and are therefore unblocked now!

[stephanos]

👋 Is there an update here?

[stephanos]

@antlai-temporal is there an update here?

[antlai-temporal]

I will refactor the WorkflowIdConflictPolicy enum in #1534.

Thanks @mjameswh !