Expand what data is saved in NWC database

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)~~