Add `ConstFeeMultiplier` to the transaction payment pallet (#12222)

* fix: FeeMultiplierUpdate

* fix: cargo fmt

* fix: rustdoc

* Revert "fix: rustdoc"

This reverts commit 96b6ad80a4cd4d856cf5a830889858c4dd4c385b.

* Revert "fix: cargo fmt"

This reverts commit 13016527bdbc53d9484642d6b52430550c0efc55.

* Revert "fix: FeeMultiplierUpdate"

This reverts commit 2cbddd0b85e0293d0eeda859807ddf70cee29067.

* feat: add ConstFeeMultiplier

* fix: use cConstFeeMultiplier in the template node