* Use Mempoolspace fees
Since bitcoind's fee estiomates are horrible, I would use an altenrative, but that adds a third party to the mix. We can either:
* Accept the risk (it is only for fee estimation anyway)
* Offer a toggle in the server settings
* Move this code to a plugin
* refactor
* Refactor
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Co-authored-by: nicolas.dorier <nicolas.dorier@gmail.com>
* BitcoinSpecificBtcPayNetwork - abstract BTCPayNetwork
* some type fixes
* fix tests
* simplify fetching handler in invoice controller
* rename network base and bitcoin classes
* abstract serializer to network level
* fix serializer when network not provided
* fix serializer when network not provided
* fix serializer when network not provided
* try fixes for isolating pull request
