resolve codepipeline quota dependency on increasing build queue quota

[greg-luxford]

… from default of 1

Issue #, if available:

Description of changes:
Ensuring no stage has more than one parallel job to prevent quota error on greenfield control tower accounts with default quota limits. First set of jobs in Build phase fail at least one job due to more than one build in queue and requires manula intervention to Retry failed resources. This prevents an otherwise unattended install.

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[versent-ms]

I performed a service limit increase on a new LZA build recently and noticed this initial failure. As the existing pipeline runtime is already at 1 hour. Removing parallel jobs I don't think is ideal and will only increase the run time. Considering this a bootstrap action and I would recommend that AWS update the documentation to suggest this to be a prerequisite.
There has been others who have also complained about long run time of the pipeline EG #266

[greg-luxford]

In this case, it is reducing the one set of jobs from 3 to 2. In context, the time taken to complete the job is 2 minutes on a 2 hour pipeline. Given the interruption caused by the failed job, coupled with the roughly 4 day lead time to obtain a quota increase, arguably this would be determined to be less impactful. Myself and my colleagues have all had similar wait times for lead time on this quota increase. The goal should be to adopt the solution broadly and at scale which should ideally cater to the default quota limits being applied to a greenfield deployment in my opinion.

[sharuzzaman]

I was just recently installed landing zone accelerator on a totally new account, and was hit by this issue. While retrying the failed build is not that hard, but having to wait for it to fail and retry increase the time taken to complete the deployment.

I fully support this patch, or if the system can be made more "intelligent", it should check how much quota that account has, and make decision to either run in sequential or in parallel.