Write Release Guide for opentelemetry-exporter-go

[RichVanderwal]

In the last few releases, important steps have been skipped. Let's write a release document that at least covers these items:

• Setting the version number here and perhaps in other places for usage tracking.
• Merging PRs
• Editing release notes making sure each PR is represented if needed, having Product Manager review and perhaps rewriting
• Tagging release
• Testing against different datacenters
• Actually releasing
• Follow-up actions

[RichVanderwal]

First draft is finished. We'll be using it very soon. https://github.com/newrelic/opentelemetry-exporter-go/wiki/Release-Checklist