Eagerly validate and put proper metadata on search attributes for on schedule workflow action

[cretz]

Describe the solution you'd like

Today all setting of search attributes is eagerly validated and is guaranteed when retrieved from the server to have the type metadata set, except for the search attributes set on the workflow of a schedule (not to be confused with search attributes of the schedule itself). We need to bring search attributes on workflows of schedules in line w/ all others with regards to validation and metadata.

Please make sure the backwards-incompatibility ramifications are taken into account. If we eagerly validate search attributes where we didn't before, someone's automated process that creates a schedule with a future workflow and then creates search attributes is now going to fail.