Warn that helm chart-ONLY instance deployment creates a POC only configuration

What does this MR do?

Moved to MR: !2404 (merged)

Closes #3097 (closed)

Customer Success, Alliances, Support, Quality and Distribution receive a continuous flow of questions from individuals who have spent a lot of time installing GitLab on Kubernetes using only the helm charts. It is evident from these conversations that they do not understand that pure helm charts create only a POC of a GitLab instance and that production-grade Cloud Native Hybrid reference architectures do not allow for all services to be in a Kubernetes cluster. Additionally the key dataplanes of GitLab (besides Git Repository Storage) can and generally should be put on Cloud PaaS.

This section intends to send customers seeking production grade results down the correct path for the sake of their efficiency and results and for the sake of GitLab efficiency. A similar approach was successfully used by adding clear, top of page communication for the legacy manual instructions for deploying Omnibus GitLab to AWS to direct customers appropriately.

Related issues

• #3097 (closed)
• gitlab-org/gitlab#351145 (moved)

Complementary MR Cross reference to production grade install info to update root information at charts repo here: http://charts.gitlab.io

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