samples/grpc-ping-go: align with knative sample and README practices

[grayside]

Proposed Changes

• Server listens on 0.0.0.0 instead of localhost.
• Dockerfile and README should run and document all commands from the context of the sample as working directory.
• Comment cleanup in Dockerfile.
• README cleanup to improve clarity and alignment with other sample READMEs

Testing Status

• Container builds & runs locally, but I could not adapt instructions for local testing.
• Locally-build container deploys to Cloud Run on GKE via kubectl apply
• Running gRPC service successfully tested with README instructions.

[averikitsch]

If you are willing, it would be nice to update the description of this sample: "A simple gRPC server written in Go that you can use for testing."
It might be nice to give a blurb about grpc and the different components of this sample (server, client). Also why do we say "that you can use for testing."?

[grayside]

Updates address additional README improvements.

[averikitsch]

The updates look great. Thanks!

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: averikitsch, grayside

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [averikitsch]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[averikitsch]

/lgtm