feat: Support fanning out parent record into multiple child syncs

[edgarrmondragon]

Feature scope

Taps (catalog, state, stream maps, tests, etc.)

Description

The current paradigm assumes developers want to sync a child stream once for every parent record. However, it's possible that a single parent record has information to sync multiple instances of the child stream.

I think it's possible to support this in a backwards-compatible way by adding a new Stream.generate_child_contexts method:

class Stream(metaclass=abc.ABCMeta):
    def generate_child_contexts(
        self,
        record: dict,
        context: dict | None,
    ) -> t.Iterable[dict | None]:
        context = self.get_child_context(record=record, context=context)
        if context:
            yield context

    def _process_record(
        self,
        record: dict,
        child_context: dict | None = None,
        partition_context: dict | None = None,
    ) -> None:
    # Update this method to use `generate_child_contexts`

There's a user in Slack that would need this to build their tap.