Expose default sequence of payload converters for custom converter creators

[cretz]

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

Right now this is buried in the default constructor, but people may want this list for other reasons

Describe the solution you'd like

Make the list available

[cretz]

Also, just make creating a data converter (and payload converter) with a different encoding payload converter prepended to the default list easier. Maybe something like temporalio.converter.default().with_encoding_payload_converter(....