[Task]: Go SDK portable logical type support

What needs to happen?

Logical types defined in https://github.com/apache/beam/blob/master/model/pipeline/src/main/proto/org/apache/beam/model/pipeline/v1/schema.proto are not supported in Go SDK. This prevents Go SDK to use schema transforms in a meaningful way.

Currently, only PYTHON_CALLABLE appear to be supported,

https://github.com/apache/beam/blob/1318bfe2039aa3d5b421bf1f23f9fcc338916750/sdks/go/pkg/beam/transforms/xlang/python/external.go#L42

however, through a different mechanism. Likely we need to first implement a framework for portable logical types in Golang, then implement each of them

Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

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