Edit the Trusted Clusters guide for Cloud

See #10633

- Misc style/grammar/clarity tweaks
- Turn the Teleport Node Tunneling Admonition into a Details
  box so it can be invisible for Cloud users. In Cloud, Nodes
  must connect via Node Tunneling.
- Use Tabs components to add Cloud versions of CLI commands
- Only show the static join token method for self-hosted users
  via Tabs
- Use a Details box to show content relevant only for Enterprise
  and Cloud users
- Remove an Admonition that was duplicated in the Troubleshooting
  section