Do not validate seat count when license is cloud-enabled

This addresses customers-gitlab-com#5784 (closed)

What does this MR do and why?

This MR skips validation of seat count whenever we're dealing with a cloud-enabled license. For more context, please refer to customers-gitlab-com#5784 (closed).

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Set up a cloud-enabled subscription with true-ups (e.g. create a subscription with start date in the past and with less seats than what's currently used in your local instance)
2. Renew the subscription without accounting for true-ups
3. Apply the activation code
4. Verify code is valid and applied successfully

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.