Send schedule configuration in function definition, not request

[mwaskom]

This PR moves the schedule configuration into the Function definition; previously it was send as an additional field in the FunctionCreateRequest. Storing it in the definition allows us to make schedule updates atomically with the rest of function deployment.

Depends on #2328

Backward/forward compatibility checks

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Check these boxes or delete any item (or this section) if not relevant for this PR.

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Note on protobuf: protobuf message changes in one place may have impact to
multiple entities (client, server, worker, database). See points above.

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Changelog

• Fixed a bug where app rollbacks would not restart a schedule that had been removed in an intervening deployment.