Join queries never get an index

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For a Join query, no index will ever be created even if a subscriber column, or location column(s) are present.

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Options here are to be a bit greedy on index creation (create an index if there's anything which resembles these columns, even with a suffix), allow specifying indexes to be created (in which case do we want to allow a bit more flex here and allow specifying the type of index?), do some juju and create the indexes that would have been created on the joinee queries.