Feat: show in settings/about which source backend LDK is using

I'de like to see/know which source backend my LDK node is using for on-chain operations, whether it is esplora, electrum or bitcoind and which host.

Maybe would albo be nice to allow to edit and set your own, most good wallets allow the user to connect to their chosen electrum server for example -> separate issue for that #1985 