Create guidelines for upgrading GitLab Runner on OpenShift

Overview

Add documentation that provides guidelines for upgrading GitLab Runner on OpenShift. The documentation should also address the scenario where a customer is updating the version of the Open Shfit cluster.

Background

1. In this issue a customer reported that an upgrade of OpenShift from v4.8 to v4.9 was blocked due to an error that the GitLab Runner Operators
2. Another customer opened a support ticket requesting guidance on how to upgrade.

Other notes

We should consider creating a support matrix for GitLab Runner Operator and Open Shift versions.