Move the examples to a separate Go module

Feature

With the recent switch to go-swagger (#6735), the grpc-gateway dependency tree has become rather large; would it be possible to move the examples to a separate submodule? This would drop 38 dependencies from the main go.mod, helping all dependants.

(This shows up in Kubernetes where we prefer our own OpenAPI modules to go-openapi; see https://github.com/kubernetes/kubernetes/pull/141360.)