[tracking]: Add Invoice Interceptor functionality

[dstadulis]

Invoice interceptor sub-saga code

• lnd
  - [6/5]: invoice+rpc: add exit hop InvoiceAcceptor sub-systems and RPC calls lightningnetwork/lnd#8771
• tapd
  - [custom channels 4/3]: add traffic shaper and invoice manager implementations #912

[guggero]

Fixed by merging both PRs.