Transactions get strangely stuck on Alfajores tx pool

[piersy]

Running just the send fee currency tx with explicit gas fields and check receipt e2e test against alfajores results in strange behaviour.

Sometimes this test was sending transactions with a 0 tip depending on the exchange rate of the fee currency used in the transaction. When that happens the test times out, I assume that a 0 tip is not permitted even if that is the result of converting a 1 wei celo tip to a fee currency tip. Note that the failed send is not a problem with the maxFeePerGas as the test uses 10x the previous block base fee to ensure it is always high enough.

Even when at least a tip value of 1 is enforced for subsequent runs of the test, they fail with the error "replacement transaction underpriced", but looking into the transaction pool with the rpc txpool_content reveals no transactions from the address used in the test. Sending a high gas price transaction fixes this, but we need to understand why that transaction is not shown in the txPool and understand better what happens with a tip of 0.

This was observed running our e2e tests against alfajores with celo-v2.0.0-rc3 deployed on the fullnodes and 9e0a1b0 deployed on the sequencer.