Split by operation

[monkeydeus]

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

Azure APIM service displays its API operations per operation. It would be more understandable and manageable if the redocly split output matched the display of the api in APIM (and other UIs as well of course)

Describe the solution you'd like

allow a cli argument or config property that will result in a distinct yaml file for each operation