Adding new API to get Public key by address

[b00f]

Describe the problem

Recently, we have indexed public keys by their addresses: #437
This helps reduce the size of blocks by removing duplicated public keys. Now, we can add a new API in gRPC to get the public key associated with a specific address.

Ideal Solution

We should add a new RPC function named GetPublicKey in blockchain.proto. It will accept an address as input and return the corresponding Public Key as output. If the public key is not indexed yet, it can return a NotFound error.

[kehiy]

I will work on this

[b00f]

I will work on this

This issue depends on #437. Please wait until that pull request is merged.

[kehiy]

@b00f indexing pubkey is merged now.
what we can do with this issue?

[b00f]

yes, now we can fix this issue.

[b00f]

Don't forget to add this API to grpc-gateway.config.yaml