[stacks-signer] Observe the bitcoin blockchain and resubmit tx's if fees spike

[jferrant]

Description

Signers may have transactions fail because of a fee spike right after submission. Monitor the mempool and resubmit any transactions that have too low fees (up to the fee limit)

Expected Approach

Query the mempool for specific pending txids (these should be known due to local signer state) Compare each txid to the amount its been in the pool vs its current fee vs the current fee rate. Resubmit the tx if necessary with higher fee and be sure to resubmit any child transactions

Acceptance Criteria

• [ ] PR adds the feature ...