Add base layer transaction type for API

[pavitthrap]

Right now, if a particular transaction comes from the base chain, the type of that payload is lost (for example it's unclear that a specific tx is a DepositFt operation).

The API currently determines that a tx comes from the base layer by checking if the raw_tx field is set to 00.

We can add a field to the transaction info called base_chain_payload_type with a type along the lines of Option(BurnchainOperation). Adding this would allow the API to easily determine the base layer tx type.

This change would also be helpful for the stacks-blockchain too.