[tracking]: `lnd/lnwallet` saga

[dstadulis]

Review and ship PRs:

• [3/5]: multi: add new AuxFundingController for custom external funding flows  lightningnetwork/lnd#8622
• [4/5]: lnwallet: add new AuxSigner interface to mirror SigPool  lightningnetwork/lnd#8632
• [5/5]: lnwallet: extensions to aux leaf store to integrate custom channels lightningnetwork/lnd#8641
• [6/5]: invoice+rpc: add exit hop InvoiceAcceptor sub-systems and RPC calls lightningnetwork/lnd#8771

[guggero]

Fixed with the merge of lightningnetwork/lnd#8771.