expose ETCD_QUOTA_BACKEND_BYTES to increase the value if needed

1. Proposed title of this feature request
expose ETCD_QUOTA_BACKEND_BYTES to increase the value if needed

2. What is the nature and description of the request?
v is limited to 7 respective 8 GB in size (depending on the OpenShift 4 version) and can't be changed if needed. Apparently there may be cases where etcd is growing quickly and building a new OpenShift Container Platform - Cluster is sometimes not possible in quick and efficient manner (specifically if running out of hardware for example). Even though the recommendation is to build a new OpenShift Container Platform 4 - Cluster when the quota size is close to be reached, we need to make sure OpenShift Container Platform - Cluster remain available even with fast growth and thus need to have the ability to adjust ETCD_QUOTA_BACKEND_BYTES to prevent business impact from happening.

3. Why does the customer need this? (List the business requirements here)
In environments where etcd is growing quickly, it's not always possible to bring up a new OpenShift Container Platform - Cluster to shift some of the workload and thus ease the pressure on etcd. Hence to avoid a disaster from happening, it would be required to be able and adjust ETCD_QUOTA_BACKEND_BYTES. Certainly customers would need to be aware about the impact of changing this and we might eventually limit the value allowed for ETCD_QUOTA_BACKEND_BYTES to some threshold. But it should be possible to adjust these settings as otherwise customers might be facing production issues.

4. List any affected packages or components.
etcd