Track exposure of all distinctly generated addresses.

[nuttycom]

In the case that this upsert is triggered by a note that was received in a pool that the conflicting row's address does not contain, we should upgrade the row to contain that receiver (similar to what we do in zcashd), because this is evidence of that receiver being exposed to the ecosystem. It's not technically evidence of other receivers in address being exposed, so we might only want to add the one receiver triggering the upsert to the conflicting row.

Originally posted by @str4d in #1673 (comment)

The above suggestion is one way to go about this, but we might want to instead consider that if multiple addresses have been generated by different wallets at the same account identifier and diversifier index, we should probably not overwrite the address that has been generated by the current wallet, but should perhaps store it separately? In any case, this requires some more consideration.