Add docs to help choose the best GitLab installation method

• Documents Installaltion
• Follow-up from: #XXX, !YYY

New doc or update?

• New documentation
• Update existing documentation

Checklists

Product Manager

• Add the correct labels
• Add the correct milestone
• Indicate the correct document/directory for this feature
• Fill the doc blurb below

Documentation blurb

• Doc title

  Installation

• Feature overview/description

  Add docs to help choose the best GitLab installation method

• Feature use cases

  The Support team are seeing many inappropriate installations of GitLab in Kubernetes (e.g. customers with only a few users). This leads to customers getting a bad experience from GitLab and uses a lot of Support time. The docs do not currently explain the limitations of installing GitLab in Kubernetes. Most customers would be best served with an Omnibus install.

Developer

• Copy the doc blurb above and paste it into the doc
• Write the tutorial - explain how to use the feature
• Submit the MR using the appropriate MR description template