Merge pull request #1826 from TheBlueMatt/2022-10-idempotency-err

Add a separate PaymentSendFailure for idempotency violation

diff --cc lightning-invoice/src/payment.rs
Simple merge

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_test_utils.rs
Simple merge

diff --cc lightning/src/ln/functional_tests.rs
Simple merge

diff --cc lightning/src/ln/payment_tests.rs
Simple merge