Fix TenantCapacity usage

[allanrogerr]

Issue

The current usage of the TenantCapacity component works on the formula capacity_usage/capacity_raw.
capacity_usage is the sum of all the used space on all disks as calculated by the madmin.AdminClient.StorageInfo function
capacity_raw is the sum of all the PVC capacities on each volume on each server.

Since capacity_usage can be greater that capacity_raw, the resulting TenantCapacity component will show 100% usage, visually showing the tenant as out of storage.

Fix

A better comparison would be capacity_usage/(capacity+capacity_usage) where capacity is the sum of all the available space on all disks as calculated by the madmin.AdminClient.StorageInfo function.

Test

Create a MinIO operator tenant.
Create and populate a bucket.
Observe the TenantCapacity component correctly indicate the proportion of usage of the available storage; and not exceed 100% while approaching it.

[shtripat]

LGTM. Verified.
May be a new PR to fix text version of Usable Capacity

[ramondeklein]

@allanrogerr Does this also need to be fixed in Enterprise console?

[allanrogerr]

@allanrogerr Does this also need to be fixed in Enterprise console?

Yes. I will also add release notes.