Expose send_payment_for_bolt12_invoice

Expose send_payment_for_bolt12_invoice

UserConfig::manually_handle_bolt12_invoices allows deferring payment of
BOLT12 invoices by generating Event::InvoiceReceived. Expose
ChannelManager::send_payment_for_bolt12_invoice to allow users to pay
the Bolt12Invoice included in the event. While the event contains the
PaymentId for reference, that parameter is now removed from the method
in favor of extracting the PaymentId from the invoice's payer_metadata.