Bug: ietf-yang-push-revision: make "revision" leaf mandatory to align with draft-ietf-netconf-yang-notifications-versioning-14

[rodonile]

https://github.com/network-analytics/NetGauze/blob/main/crates/netconf-proto/src/yang_push/subscription.rs#L980-L981

https://datatracker.ietf.org/doc/html/draft-ietf-netconf-yang-notifications-versioning