Add L3 support for Forwarding rule namer

[TortillaZHawaii]

Current implementation isn't able to simply add l3_default to the resource name as underscores are not allowed in the name. We can shorten the protocol to l3 to prevent that. It also doesn't take too much of the string that has to also fit service name and namespace.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @TortillaZHawaii. Thanks for your PR.

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[TortillaZHawaii]

/assign @mmamczur

[sawsa307]

/ok-to-test