Allow to set `SendingParameters` in BOLT12 send methods

[tnull]

In #336 we added support for specifying SendingParameters for BOLT11 and spontaneous payments.

Unfortunately, the BOLT12 API currently doesn't allow to specify these fields, but we should also add them to BOLT12 sending methods once it becomes available in LDK (see tracking issue lightningdevkit/rust-lightning#3262)

[tnull]

This will be unblocked by #462. We should consider whether we can drop our SendingParameters for the upstream RouteParametersConfig