Story: As a Quay administrator I would like to leverage human-readable storage capacity units so I can script against the quota management API more effectively.

Acceptance criteria:

• add a new field called limits which optionally accepts a string representation of a human-readable storage capacity
• SI units like Mi, Gi or Ti should equally be allowed like non-standard units like GB or MB
• the use of the limit field should be mutually exclusive with the use of limit_bytes
• the change should be made in the namespace and superuser quota management API in a backwards-compatible fashion