Automatic merge from submit-queue (batch tested with PRs 50094, 48966, 49478, 50593, 49140)
[kube-proxy] Move UDP conntrack operations together to pkg/proxy/util/conntrack.go
**What this PR does / why we need it**:
Fix TODO in pkg/proxy/iptables.go, see
https://github.com/kubernetes/kubernetes/blob/master/pkg/proxy/iptables/proxier.go#L1632
Move UDP conntrack operations together to from `pkg/proxy/iptables/proxier.go` to `pkg/proxy/util/conntrack.go` so that make them more consistent and add some UTs.
**Which issue this PR fixes**
Fixes#49477
**Special notes for your reviewer**:
```release-note
NONE
```