Implement IndexTransactionHandler

[theanmolsharma]

The goal of this issue is to complete

    async execute(command: IndexTransactionCommand) {
        throw new Error(`Method not implemented. Command: ${command}`);
    }

in src/handlers/commands/index-transaction.handler.ts.

execute() should do the following:

• Perform the following checks:
  • verify if the transaction contains at least one BIP341 P2TR output. This output could be a potential silent payment.
  • verify if the transaction contains at least one input from the Inputs For Shared Secret Derivation list.
  • verify that the transaction does not spend an output with SegWit version > 1
• Calculate scan_tweak as described in design.md.
• Save everything to db