Add note about allowed overage

What does this MR do?

With #333851 (closed) we updated the renewal and true-up flows to allow a 10% overage like we already did for new subscriptions. If the number of billable users does not exceed 10% of the total number of users in the subscription purchased (either for renewal or mid-term add-ons), the license file should be applied and the instance activated. The overage should be paid with the next true-up.

This MR adds details to the docs about that allowed overage when applying a license.

Related issues

#333851 (closed)

Author's checklist

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