Waste of previous BTC checkpoint transactions when new UTXOs are spent

[gitferry]

This issue is brought up by @vitsalis as follows.

Lately BTC fees have become super volatile, leading to us having UTXOs stuck in the mempool. More particularly, the following scenario happens: we submit a transaction with a reasonable fee based on the estimation based on the current mempool. A lot of BTC transactions come along and they continuously raise the fees. Our transactions are stuck in the mempool and therefore unspent. Typically, we combatted this issue by having many available UTXOs, but this does not seem to be enough, as lately a transaction might get stuck in the mempool for weeks. Currently, on our testnet, we do not have any checkpoints for 4 days due to only having two available UTXOs both of which are stuck. Clearly, this is not maintainable.