Add a runbook on how to trigger internal release pipeline's individual stages when needed

Background

When running the chatops command to trigger the internal release process (ex: /chatops run release internal), the following are created:

1. A release task issue
2. An internal release pipeline (where we pass the pipeline variables from the InternalRelease::Issue class)

Problem

If a pipeline fails during the early stages, release managers can continue either:

• Creating a pipeline for the individual failed stages, or
• Creating the entire pipeline (resuming from where it left off)

This manual process requires correctly setting the needed pipeline variables similar to the ones passed by the InternalRelease::Issue class.

Proposed Solution

Update the release manager runbook to document:

1. How to identify required pipeline variables for internal releases
2. How to create a new internal release pipeline manually (either using individual stages or the entire pipeline)