examples: Add GCP CSM Observability example

[DNVindhya]

This PR adds a CSM Observability example. This is intended to be built as docker images and deployed as part of CSM observability user guide.

[ejona86]

We should use jib. As in another example:

grpc-java/examples/example-hostname/build.gradle

Lines 61 to 69 in 791f894

	jib {
	from.image = "gcr.io/distroless/java17-debian12"
	container.ports = ['50051']
	outputPaths {
	tar = 'build/example-hostname.tar'
	digest = 'build/example-hostname.digest'
	imageId = 'build/example-hostname.id'
	}
	}

If we want, we can have the dockerfile as well, but we shouldn't root it in grpc-java but instead expect it to be built in the example-gcp-csm-observability directory.

[DNVindhya]

As this is related to automating container image generation, I will add it in a separate PR.

[ejona86]

Well, it was more I don't want us to use Dockerfile because they are harder to integrate and produce worse results. But since you've gotten the Dockerfile approach working, I guess that's fine... but... yeah, I had wanted us to push jib in the documentation.

[ejona86]

Fix up the comment style, then LGTM

[ejona86]

Well, it was more I don't want us to use Dockerfile because they are harder to integrate and produce worse results. But since you've gotten the Dockerfile approach working, I guess that's fine... but... yeah, I had wanted us to push jib in the documentation.