Make Lightning App not dependent on local Bitcoind (Neutriuno mode)

[ffrediani]

trafficstars

Currently in order to install Lightning on Umbrel it is necessary to install Bitcoin Node first and wait for it to sync, but there may already be a Bitcoin Code available and synced nearby or the user may just prefer to use a public node.

Therefore making Lightning App installable without depending on Bitcoin Core can be useful for such cases and improve user experience.

In the case it detects there is no Bitcoin Node installed locally it can warn the user that without connecting to a Bitcoin Node it is not possible to operate and then have options on Lightning App configuration that allows the user to configure Neutrino mode (bitcoin.node=neutrino), connect to an external node (neutrino.addpeer=<your Bitcoin node's IP address>:<p2p port>) and adjust the variables blockfilterindex=1 and peerblockfilters=1

Ref: https://docs.lightning.engineering/lightning-network-tools/lnd/enable-neutrino-mode-in-bitcoin-core