Expand what data is saved in NWC database

[rolznz]

Do some planning around:

• What are our current limitations/state and where are we trying to get to (better notifications for users, better app connection budgets, improved performance, less app complexity)
• Transactions - currently we only store payments, not invoices. and no metadata, status, fees
  • Do we want to have one table for both payments and invoices? e.g. "Transactions" table as that's what it's called in NIP-47
  • improved budget requirements (fees, payment state)
  • custom data (LUD-12, LUD-18) and custom TLVs (Podcasting 2.0)
  • timing info (created, updated)
  • bolt11 invoice
  • payment hash (should be unique)
  • correct indexes and constraints
• Can we undo ALL our changes to the LDK-node payment table - this is difficult to maintain and will cause migration issues
• Channels - currently we only have access to open channels through LDK - closed ones disappear
  • How to fetch the data and when
  • Additional state - like if it closed, why
  • What to do with existing channels
• DB size issues (my nwc.db is 400+mb already)

[rolznz]

This changes at a higher level because NIP-47 requests would go to our database, which impacts all our lnclients.