Update docs to mention updated requirements for COS on satellite

[nerdingitout]

I learned that the documentation for COS on Satellite requires a few updates and changes to make provisioning the service an easier experience. Kindly review my suggestions:

• The note in this section Object Storage for Satellite requires OpenShift 4.7. is outdated since the oldest openshift version is 4.8 as far as I know + the end user isn't responsible for provisioning openshift cluster for the service, therefore it might add some confusion to the user when reading the docs.
• Add OS host requirement to the "before you begin"/prerequisites section, so the end user won't go through the same trouble of provisioning the hosts with the wrong OS. Satellite currently supports the following OS: RHEL7, RHEL8, and CoreOS. However, COS on Satellite only supports RHEL7. If the user isn't aware of this requirement then they might go for RHEL8. I actually happened to do this because I thought whatever OS Satellite supports, COS will support by default as well.
• I think it would be relevant to add a section on the same page clarifying the supported storage templates by COS, I understand that COS supports mostly all of them but it would be helpful since not all storage templates were tested/are supported.
• Images are missing the docs, please fix that.

Kindly review my request and hope you find it helpful. Thank you in advance!

[dpdresse]

The topic includes one image for the UI and this is currently showing in the topic dated 12/01/21: https://cloud.ibm.com/docs/cloud-object-storage?topic=cloud-object-storage-provision-cos-satellite#provision-satellite-assign .