Change the bucket disk io priority to low as Default

The UI already presents High priority as the default choice but this message should be reinforced in documentation as well that low priority setting should not be used as default choice.

Using low priority as the default choice for buckets adversely impacts bucket performance. For example if there are 8 low priority buckets and 1 high priority bucket, then the 8 low priority buckets have a throughput of 30-40% of the high priority bucket.

This also means that there should not be a case where the customer has only Low priority buckets since all buckets suffer from decreased performance in this case.