Redirect Kubernetes installation to the charts docs

What does this MR do?

Redirect Kubernetes installation to the charts docs.

I redirected all links under doc/install/kubernetes/ to the respective pages of the charts. I only left the content of doc/install/kubernetes/index.md for another MR, since it also contains some Runner info, which is being tackled in gitlab-runner#2964 (closed).

Current tree list:

├── gitlab_chart.md
├── gitlab_omnibus.md
├── gitlab_runner_chart.md
├── index.md
└── preparation
    ├── connect.md
    ├── eks.md
    ├── networking.md
    ├── rbac.md
    ├── tiller.md
    └── tools_installation.md

Old URL	New URL	Old URL has comments?	New URL has comments?	Manual redirect or identifier
https://docs.gitlab.com/ee/install/kubernetes/gitlab_chart.html	https://docs.gitlab.com/charts/index.html	yes (21)	no	manual
https://docs.gitlab.com/ee/install/kubernetes/gitlab_omnibus.html	https://docs.gitlab.com/charts/index.html	yes (19)	no	manual
https://docs.gitlab.com/ee/install/kubernetes/gitlab_runner_chart.html	https://docs.gitlab.com/runner/install/kubernetes.html	yes (17)	yes (21)	manual
https://docs.gitlab.com/ee/install/kubernetes/index.html	-	yes (7)	-	-
https://docs.gitlab.com/ee/install/kubernetes/preparation/connect.html	https://docs.gitlab.com/charts/installation/cloud/index.html	no	no	-
https://docs.gitlab.com/ee/install/kubernetes/preparation/eks.html	https://docs.gitlab.com/charts/installation/cloud/eks.html	no	no	-
https://docs.gitlab.com/ee/install/kubernetes/preparation/networking.html	https://docs.gitlab.com/charts/installation/deployment.html#networking-and-dns	yes (2)	no	identifier
https://docs.gitlab.com/ee/install/kubernetes/preparation/rbac.html	https://docs.gitlab.com/charts/installation/deployment.html#rbac	no	no	-
https://docs.gitlab.com/ee/install/kubernetes/preparation/tiller.html	https://docs.gitlab.com/charts/installation/tools.html	no	no	-
https://docs.gitlab.com/ee/install/kubernetes/preparation/tools_installation.html	https://docs.gitlab.com/charts/installation/tools.html	no	no	-

Important

We don't know how comments will behave if both old and new URLs have comments https://gitlab.com/gitlab-com/gitlab-docs/issues/357.

We'll probably need to manually update the links in Disqus following the steps in https://gitlab.com/gitlab-com/gitlab-docs/issues/357#workflow, and providing the following CSV:

https://docs.gitlab.com/ee/install/kubernetes/gitlab_chart.html, https://docs.gitlab.com/charts/index.html
https://docs.gitlab.com/ee/install/kubernetes/gitlab_omnibus.html, https://docs.gitlab.com/charts/index.html
https://docs.gitlab.com/ee/install/kubernetes/gitlab_runner_chart.html, https://docs.gitlab.com/runner/install/kubernetes.html

Related issues

We need to first merge gitlab-runner!1250 (merged).

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/58870

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the ~Documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set and that you merge the equivalent EE MR before the CE MR if both exist.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.