Add way to add a label to lightning transactions

[rolznz]

sometimes you can pay invoices that have no memo and then later look back and not sure what the payment was about. I think we should possibly use the transaction metadata field for this

[im-adithya]

This was also an asked feature in Alby Go, would be great to have this in both places. Linking getAlby/go#166

(cc @pavanjoshi914 for the extension)

[rolznz]

It should be possible with metadata (make_invoice and pay_invoice both support the metadata property). Here is what we currently have CC @bumi

[MoritzKa]

For bookkeeping we need the following information per transaction:

• description field: So I can fill in the purpose. For example: top up PPQ.AI account
• counterparty field: So I can fill in the vendor's or customer's name such as PPQ.AI
• account field: So I can fill in the account such as sponsoring, merchandise or contractor or alternatively GL-codes that represent these accounts.
• transaction type field: For example expense for the PPQ.AI top up or deposit, sales receipt, transfer, etc.

(if the description field is labeled well, I could deduct all other information in a manual way)

That would be a huge improvement!

[rolznz]

• label should be separate from description (cannot rely on this)
• learn from the labels BIP / see how it should be added to our metadata

[rolznz]

https://bips.dev/329/