K8s auto-instrumentation details and example (Node.js)

[eedugon]

Adding document docs/kubernetes/operator/instrumenting-nodejs.md with details for instrumenting Node.js applications on kubernetes with the EDOT Node.js and the operator.

@trentm , if possible I'd like your review on this:

• Check if we should add extra details to the file.
• I haven't described the details of how auto-instrumentation for Node.js is performed under the hood. (because I haven't tested it myself), but I think it's always useful as it helps with troubleshooting. Do you know how this is done? I assume it might be with an init container to copy the SDK to a shared volume plus a configuration in the main container to use the SDK through NODE_OPTIONS env var, but I'm not sure.

This PR is similar similar to:
#54 (Java)
#58 (Python)

[eedugon]

@trentm , thanks a lot for your review here.
When merging java and python specific docs I got a lot grammar related feedback from Mike that I hadn't applied here, so I'm going to rewrite a bit this PR to apply also the improvements made in the other PRs.

I will consider everything you have mentioned here, but in some of the topics we had already changed those sentences (sorry I hadn't told you before about it).

I'll ping you and make comments as soon as I apply the changes. Thanks a lot!

[eedugon]

Thanks a lot @trentm for your help here! I think we are ready for merging / final review.

FYI I have removed also the kubectl port-forward hint as we can assume users know how to generate traffic to their apps.