DAPI getIdentityByPublicKeyHash is not working for masternode identities

[pshenmic]

Expected Behavior

DAPI GRPC query for searching an identity by specific public key hash should work for all identities in the state.

Current Behavior

Masternode identity could not be found through getIdentityByPublicKeyHash RPC, query always returns Not Found error.
Regular identities can be found just fine.

The query should work transparently to the user independently which type of identity he tries to retrieve

Possible Solution

Steps to Reproduce (for bugs)

1. Get identity via masternode identity's identifier
2. Get first public key from the set
3. Try to search the given identity by that specific public key
4. Query throws Not Found error

Context

Due recent changes in the code, masternode identities now behave differently from the regular ones, and that breaks getIdentityPublicKeyHash GRPC query.

Your Environment

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[shumkov]

I believe it's by design rather than a bug. The getIdentityByPublicKeyHash endpoint works only for unique keys, but masternode keys aren't unique. Please @QuantumExplorer confirm. @thephez shall we document it somehow?