Changes to HA docs to inc different architecture types

What does this MR do?

Resolves part of https://gitlab.com/gitlab-org/gitlab-ce/issues/44800.

Points of interest

• We can backport to CE later
• Adds the tier badge for each section (Core, Premium) as appropriate.
• Create two top-level headings, one each for Scaled and HA.
  • Mentions relevant architectures with links at the top of each section
  • Links back to the relevant sections at the bottom of each section
• Trying to keep to a minimal viable change
  • Add scaling sections. Link to each from the 'Basic Scaling' section on the index page.
  • Wait to complete other scaling and HA installation instructions for later iteration.
  • Avoid major changes to the HA sections except for changes to heading depth. Fully-knowing that these sections need some updates, too. Let's keep that for a later iteration.
  • Even with these in mind, the changeset here will be quite large
• Use the review app links to see the changes visually

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer