feat: [datastore] new module for datastore

[cloud-java-bot]

Generated by @diegomarquezp via generate_new_client_hermetic_build.yaml

Command used:

python generation/new_client_hermetic_build/new-client.py add-new-client --api_shortname="datastore" --proto-path="google/datastore/v1" --name-pretty="Datastore API" --product-docs="https://cloud.google.com/datastore" --api-description="Datastore is a highly scalable NoSQL database for your web and mobile applications."

docker run --rm \
  -v repo-google-cloud-java:/workspace/google-cloud-java \
  -v /tmp:/tmp \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e "RUNNING_IN_DOCKER=true" \
  -e "REPO_BINDING_VOLUMES=-v repo-google-cloud-java:/workspace/google-cloud-java" \
  gcr.io/cloud-devrel-public-resources/java-library-generation:latest \
  python /src/generate_repo.py generate \
  --generation-config-yaml=/workspace/google-cloud-java/generation_config.yaml \
  --repository-path=/workspace/google-cloud-java \
  --target-library-api-shortname=datastore