Add quotas for Server Groups (quota checks)

This third change in a sequence that adds new quota values
for server groups, which implements the quota checks.

Co-authored-by: Cyril Roelandt <cyril.roelandt@enovance.com>

Implements: blueprint server-group-quotas
DocImpact

Change-Id: I535c4ac2475d0b0ca6e14081f92e1c7d111792bd
Merge "Add quotas for Server Groups (quota checks)"