aiplatform: add implementation for v1beta1

[alethenorio]

Is your feature request related to a problem? Please describe.
There's a big push right now for the new Vertex AI platform for building MLOps, all of which have APIs under the aiplatform package however using the apiv1 package which is the only one implemented here just returns unimplemented. Using python SDK works without any issue. I get a feeling this is because the current implementation of most APIs live under the v1beta1 protos. It is very hard for us who have an entire organization working in Go to have to fallback to python SDKs or start implementing the REST APIs by hand.

Describe the solution you'd like
Have an implementation for the v1beta1 protos of aiplatform package

Describe alternatives you've considered
Building a REST API by hand or falling back to python SDKs

Additional context

[codyoss]

@alethenorio Thanks for this feedback. I will do some research here and get back to you. If other languages have published this API already, it might just be an oversight that we don't have it yet in Go.

[alethenorio]

@codyoss Thank for the quick response here. Can also confirm that I was able to call the APIs using the genproto repo directly with v1beta1 protos. Looking forward to this release