RPC-465 adding optional flag to include 0 for every slot there is no transaction

[dmitriy-helius]

Overview

• Client complained that they were paying too high of fees. Analysis shows that the account they were querying has almost no transactions. The decision was made to add a flag that clients can use to add zero to slots with no transactions.
• The flag will be false by default not to impact others

Testing

• Unit testing
• Local testing