Query should be sign-able

[janaakhterov]

Currently queries and transactions are mostly distinct on the fact a transaction is sign-able, while a query is not. This doesn't make sense as a query has a payment transaction within it, and should allow those payment transactions to be signed by multiple keys if necessary.

If both transactions and queries are to now going to be sign-able, perhaps this code could be abstracted away into a new private type called Request, or we could shove this into Executable like we did for nodeAccountIds, but I'm not a big fan of that.
This is what I have in mind

abstract class Request<SdkRequestT extends Request<SdkRequestT, ProtoRequestT, ResponseT, O>, ProtoRequestT, ResponseT, O>
    extends Executable<SdkRequestT, ProtoRequestT, ResponseT, O> {

    public abstract SdkRequestT freezeWith(@Nullable Client client);

    public SdkRequestT freeze() {
        ...
    }
    
    public final SdkRequestT sign(PrivateKey privateKey) {
        ...
    }

    public SdkRequestT signWith(PublicKey publicKey, Function<byte[], byte[]> transactionSigner) {
        ... 
    }

    public SdkRequestT signWithOperator(Client client) {
        ...
    }

    public SdkRequestT addSignature(PublicKey publicKey, byte[] signature) {
        ...
    }

    public Map<AccountId, Map<PublicKey, byte[]>> getSignatures() {
        ...
    }
}

We could move most of the functionality from Transaction into this new Request type which would simply both Transaction and Query. For instance currently Transaction has these fields

    protected List<com.hedera.hashgraph.sdk.proto.Transaction> transactions = Collections.emptyList();
    protected List<com.hedera.hashgraph.sdk.proto.SignedTransaction.Builder> signedTransactions = Collections.emptyList();
    protected List<SignatureMap.Builder> signatures = Collections.emptyList();

If we move these fields into Request then Query can treat transactions as the payment transactions, while Transaction continues treating these fields as normally does.