Implement RegionalExternal loadbalancer type

[DvdChe]

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/kind feature

Describe the solution you'd like Due to technical constraints, I'm unable to deploy a global load balancer. As a result, I need to use a regional one by setting the GCPCluster.spec.loadBalancer.loadBalancerType field to either RegionalExternal or RegionalExternalInternal.

Anything else you would like to add: [Miscellaneous information that will assist in solving the issue.]

I already implemented the feature here

To do it so i had to rebuild the GoogleCloudPlatform/k8s-cloud-provider because published releases do not provides interfaces for regional tcp proxy loadbalancer or i did not succeed to find the right release ? Last release provides the regional backend tcp proxies

f you think this could be eligible for a pull request, I'm happy to work on adding tests and ensuring the code is clean.