Docs Release: no-downtime docs site release (blue/green amplify deployment)

currently, when deploying the EKS-A docs, the docs site goes down for a short period while the branch is changed. We should modify the docs site deployment process for a no-downtime docs deployment.

Start by tracing the EKS-A docs deployment process and the branch-change step described in the issue. Identify the current Amplify deployment entry point and define a blue/green flow that keeps the docs site available; done means a docs release completes without downtime.

Written by the indexing model from the issue text.