[Feature Request] Eager workflow start

[antlai-temporal]

Is your feature request related to a problem? Please describe.

Support for Eager Workflow Start was added in the server in 1.20, and is currently supported in Java and Go SDKs. It
reduces the latency to start a workflow by allowing the client to directly schedule the first workflow task to a local worker. See temporalio/features#242 for details.

The goal is to make Python the first core-based SDK to support Eager Workflow Start after is enabled in Core.

Describe the solution you'd like

This mechanism is mostly transparent to the Python SDK client, but we need to add a flag enable_eager_start to client.start_workflow to use it. It will default to False while the core implementation is considered experimental.

Additional context

This depends on temporalio/sdk-core#606