first attempt to export from API Gateway

[timburks]

This is a hastily-written exporter that creates API entries for each gateway in the currently-configured gcloud project. It uses gcloud to call the apigateway API (that could be replaced with direct calls). I've exported both OpenAPI and gRPC services and verified that exported results are read into the registry, but the protobuf-based specs aren't fully-resolved (they are missing common dependencies), so they won't be compilable with protoc without some additional work.

This is potentially all throwaway code, I just wanted to have something to show for API Gateway.

Usage: registry-connect discover apigateway gateways --output DIRECTORY where DIRECTORY is the directory to contain exported Registry YAML and API specs. This requires that gcloud be installed and configured to use a project that has some API Gateway instances to export.

By default it writes to gateway-export and here's what I get for a sample project with three gateways:

$ find gateway-export/
gateway-export/
gateway-export/timburks-test-shakes
gateway-export/timburks-test-shakes/info.yaml
gateway-export/timburks-test-shakes/shakes.proto
gateway-export/timburks-test-shakes/api_config.yaml
gateway-export/timburks-test-bookstore
gateway-export/timburks-test-bookstore/info.yaml
gateway-export/timburks-test-bookstore/bookstore.proto
gateway-export/timburks-test-bookstore/api_config.yaml
gateway-export/timburks-test-hello
gateway-export/timburks-test-hello/info.yaml
gateway-export/timburks-test-hello/openapi.yaml

$ cat gateway-export/timburks-test-shakes/info.yaml 
apiVersion: apigeeregistry/v1
kind: API
metadata:
  name: timburks-test-shakes
  labels:
    provider: timburks-test
data:
  displayName: timburks-test gateway shakes
  description: Exported from API Gateway
  versions:
    - metadata:
        name: v1
      data:
        displayName: v1
        specs:
          - metadata:
              name: protos
            data:
              filename: protos.zip
              mimeType: application/x.proto+zip
  deployments:
    - metadata:
        name: gateway
      data:
        displayName: gateway
        endpointURI: https://shakes-8ez1hpbl.wl.gateway.dev

[timburks]

I'll follow up with a PR that sets some labels with more detail.