Clean up docs under install/docs/ssot-installation-guides

This is an initiative to ensure all documentation complies completely
with the Documentation Style Guide section "Documentation is the single
source of truth (SSOT)" according to this epic
https://gitlab.com/groups/gitlab-org/-/epics/1280.

In particular, the changes of this commit touch all files under
doc/install/. Most notably:

- install/redis.md:
        Redirect to Redis section of install guide.

- install/pivotal/index.md:
        Changed its content to reflect the current status, which is no
        longer supported (since 2017!).

- install/google-protobuf.md:
        Incorporated inside installation.md under the troubleshooting section.

- install/openshift_and_gitlab.md:
        Clarified that this guide is no longer relevant. We might want to
        redirect to the Chart docs in the future.

- install/structure.md:
        Incorporated inside installation.md under its own section.

- install/kubernetes/index.md:
        Redirected to https://docs.gitlab.com/charts

1 files changed, 2 insertions, 38 deletions

diff --git a/doc/install/kubernetes/index.md b/doc/install/kubernetes/index.md
index fd0f7b0d328..43655767002 100644
--- a/doc/install/kubernetes/index.md
+++ b/doc/install/kubernetes/index.md
@@ -1,41 +1,5 @@
 ---
-description: 'Read through the different methods to deploy GitLab on Kubernetes.'
+redirect_to: https://docs.gitlab.com/charts/
 ---
 
-# Installing GitLab on Kubernetes
-
-NOTE: **Kubernetes experience required:**
-Our Helm charts are recommended for those who are familiar with Kubernetes.
-If you're not sure if Kubernetes is for you, our
-[Omnibus GitLab packages](../README.md#installing-gitlab-using-the-omnibus-gitlab-package-recommended)
-are mature, scalable, support [high availability](../../administration/high_availability/README.md)
-and are used today on GitLab.com.
-It is not necessary to have GitLab installed on Kubernetes in order to use [GitLab Kubernetes integration](../../user/project/clusters/index.md). 
-
-The easiest method to deploy GitLab on [Kubernetes](https://kubernetes.io/) is
-to take advantage of GitLab's Helm charts. [Helm](https://github.com/kubernetes/helm/blob/master/README.md)
-is a package management tool for Kubernetes, allowing apps to be easily managed via their
-Charts. A [Chart](https://github.com/kubernetes/charts) is a detailed description
-of the application including how it should be deployed, upgraded, and configured.
-
-## GitLab Chart
-
-This chart contains all the required components to get started, and can scale to
-large deployments. It offers a number of benefits, among others:
-
-- Horizontal scaling of individual components.
-- No requirement for shared storage to scale.
-- Containers do not need `root` permissions.
-- Automatic SSL with Let's Encrypt.
-- An unprivileged GitLab Runner.
-
-Learn more about the [GitLab chart](https://docs.gitlab.com/charts/).
-
-## GitLab Runner Chart
-
-If you already have a GitLab instance running, inside or outside of Kubernetes,
-and you'd like to leverage the Runner's
-[Kubernetes capabilities](https://docs.gitlab.com/runner/executors/kubernetes.html),
-it can be deployed with the GitLab Runner chart.
-
-Learn more about the [GitLab Runner chart](https://docs.gitlab.com/runner/install/kubernetes.html).
+This document was moved to [another location](https://docs.gitlab.com/charts/).