rpc: include_unsafe option for fundrawtransaction

Summary:
Allow RPC users to opt-in to unsafe (unconfirmed received from an external key) inputs when funding a raw transaction.

This is a backport of core#21359
Depends on D14402

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14403