base-transactions: add authorizedRegistrators property to RegisterCollection transaction

[kristjank]

Add allowed registrator property on the plugin and not on the blockchain level. This is for the intermediate term, as it helps us to centralize who is allowed to register new collections of assets on the blockchain.

{
    "authorizedRegistrators": ["PK1", "PK2",...."PKn"]
}

default value is [] - meaning anyone can send the transaction to the blockchain.

Conditions:

• if value in [""] - only allow PK in list to sendTransactions
• if value === [] - anyone can send transaction

Note

This is not an optimal solution, as it can affect the bootstrap process. We will address this in a separate issue.