How to isolate CI pipeline per-branch environments in Kubernetes?
We're working on an open source project called Jenkins X which is a proposed sub project of the Jenkins foundation aimed at automating CI/CD on Kubernetes using Jenkins and GitOps for promotion.
When you submit a Pull Request we automatically create a Preview Environment which is exactly what you describe - a temporary environment which is used to deploy the pull request for validation, testing & approval before the pull request is approved.
We now use Preview Environments all the time for many reasons and are big fans of them! Each Preview Environment is in a separate namespace so you get all the usual RBAC features from Kubernetes with them.
If you're interested here's a demo of how to automate CI/CD with multiple environments on Kubernetes using GitOps for promotion between environments and Preview Environments on Pull Requests - using Spring Boot and nodejs apps (but we support many languages + frameworks).