Regtest end-to-end test suite

[danielgranhao]

We should explore the possibility of running end-to-end tests on regtest. These would likely be time-consuming to run, but that's fine if we choose wisely when to run them.

It should be possible to set up all of the SDK's runtime dependencies (Bitcoin, Liquid, Lightning, Swapper) locally, so I don't see any reason not to have this.