docs: Describe how to fully update an instance

Description

This expands the documentation to explain how to update an instance from a local shell.

Supporting information

I'm not sure if this is correct, as I haven't gotten it working yet! But it seems close :p

Testing instructions

Steps to test the changes:

1. Run the commands to update an instance.

Dependencies

Depends on !200 (merged) if you're upgrading a Palm/nightly instance.

Screenshots

n/a

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated

Additional context

Ticket: MNG-3815