Add static invoice creation utils to ChannelManager (Blinded Paths, async payment, Bolt12, Offer)

https://github.com/lightningdevkit/rust-lightning/pull/3408

Host: vincenzopalazzo  -  PR author: valentinewallace

Notes

Questions

  1. Did you review ldk/3408? Is it a Concept ACK, approach ACK, tested ACK, or NACK?
  2. Did you review bolt/1149? Is it a Concept ACK, approach ACK, tested ACK, or NACK?
  3. What are static invoices?
  4. How does the proof of payment look like in the case of static invoices?
  5. In commit 5c0b804 why do we need to clone the RetryableInvoiceRequest?
  6. In commit 55b7d what is the AsyncBolt12OfferContext and why are we introducing it?