Add MPLS-in-UDP and GUE decapsulation actions to policy-forwarding rules

[danameme]

Add MPLS-in-UDP and GUE decapsulation actions to policy-forwarding/openconfig-pf-forwarding-policies.yang

1. MPLS-in-UDP [RFC 7510]
2. Generic UDP Encapsulation (GUE) [https://datatracker.ietf.org/doc/draft-ietf-intarea-gue/]

[github-actions]

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[dplore]

FYI: this is getting added here for afts and use in gRIBI:
#1153

Not exactly the same use case as static config though.

[robshakir]

I suspect we actually need this configuration to ensure that UDP decapsulation can be covered. I'll re-open this issue to keep it tracked -- especially with overlap with #1153.

[dplore]

This issue is similar, but different. It requests using policyforwarding, whereas #1153 only has AFT in scope.

Note, https://github.com/openconfig/featureprofiles/pull/3363/files#diff-a6b35105c1accdb1889d9c529f4a13d6844d4a9844a90f3d3f736eba728502c5R304 has a nascent proposal for decap using AFT which could use a review.