Cannot use default Replication Factor for shirt size

When using the OpenShift Console to create a LokiStack instance, the `replicationFactor` is set to 1. This is due to a default value set in the API. This causes the `replicationFactor` to be 1, regardless of what the initial default of this value is.

With the update, this field can be left empty which allows the defaults of 2 and 3 (respectively for 1x.small and 1x.medium) to be used. This field was intended to allow for overwriting the operator. However, as is, it causes the field to always be 1, which is not the intended effect.