Adjust 2k Ref Arch with latest recommendations

What does this MR do?

MR updates the 2k Reference Architecture to the latest recommendations as follows:

• Webservice pods have been switched from 2 worker to 4 worker to align with other Architectures and allow for better Puma shared memory management
• Supporting node pool on GCP upped to n1-standard-2 to align with AWS and give more room for system pods / optional monitoring
• Increase of Sidekiq workers / pods from 2 to 4 (Omnibus + Cloud Native Hybrid) to align better with other Architectures
• Switch Sidekiq node pool from 2 n1-standard-2 to 1 n1-standard-4. This seems like an academic change but the new numbers in Kubernetes don't work with a split of 2 as each node runs several small k8s services that just tip each over.

Related issues

Closes gitlab-org/quality/reference-architectures#146 (closed)

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