Add Fulcrum as Electrs alternative

[ok300]

Is your content request related to a problem? Please describe.

According to https://www.sparrowwallet.com/docs/server-performance.html#results :

Initial test: Fulcrum is 22x faster than ElectrumX, ~300x faster than Electrs
Wallet refresh: Fulcrum is 8x faster than ElectrumX, 1.5x faster than Electrs

Describe the solution you'd like

Please add Fulcrum as an optional installable app.

Additional context

• Fulcrum: the most performant Electrum Server implementation raspiblitz/raspiblitz#2924

• https://github.com/openoms/bitcoin-tutorials/blob/master/fulcrum.md

• https://www.sparrowwallet.com/docs/server-performance.html

• Mark this if you searched the existing list of open/closed issue and did not find anything similar