Explain 4007 user on fleet access page #3124
Description
The test privileged user shows up by default in production systems and is used by support (indirectly — not exactly for authentication or authorization, as far as I know), so it would be inconvenient for it to be deleted. We would like to get rid of it (oxidecomputer/omicron#2305) but in the meantime we can do some harm reduction in the UI to explain what it is. The ID is well-known, so we can just detect it and give it a special name and a tooltip.
