docs: Write guide for semi-complex multi-cluster tenancy repo structure

[Callisto13]

Part of #3502

As a WG User
Who has a one management and one+ leaf clusters and a handful (~10) of objects (apps/kustomizations/etc)
I would like to read a guide which shows me how to organise my gitops repository
According to a hypothetical tenancy model

Elements to include:

• An explanation of what the guide is for, why a user would want to follow it and a summary of the outcome
• A complete list of prerequisites
  • what state does the cluster need to be in?
  • do i need to have set anything up outside the cluster?
  • is this guide for a development environment? or do i need a "real" env with network/dns/routing etc?
• An intuitive journey through the steps
• Yaml/command output collapsed so that the page is not saturated
• Screenshots if applicable (zoom in on these please so they can actually be read)
• Tested copy-pastable commands (such as those i would run to commit things to my gitops repo)
• An example repository which shows the completed solution which users can easily clone and apply to their cluster if they want

[lasomethingsomething]

Merged the ask with #3504 #3504