Use Mib / Mebibyte as applicable

MB-23852 tracks changes in UI and ns_server to use Mib and Mebibytes (https://en.wikipedia.org/wiki/Byte#Multiple-byte_units) as they more accurately describe the memory size values.

The docs should be updated to also use the more accurate terminology. As an example, here's a case describing ramQuotaMB (which has been renamed to ramQuota - see MB-23852). The doc says:

The amount of memory to be allocated to the bucket, per node, in megabytes. The minimum amount is 100 MB. 

This should be corrected to:

The amount of memory to be allocated to the bucket, per node, in mebibytes. The minimum amount is 100 MiB. 

Note this is just one case. Here's usage when configuring the cluster

and when configuring auto-compaction