More detail in OxQL schema descriptions

[david-crespo]

The state field on virtual_machine:vpcu_usage appears to be an empty string in the schema list response

That it's empty may be a bug, because I see a description in the schema file, though it's not a very good one:

omicron/oximeter/oximeter/schema/virtual-machine.toml

Lines 75 to 77 in 7a6144b

	[fields.state]
	type = "string"
	description = "The state of the vCPU"

I am working on help copy for charts in the console oxidecomputer/console#2714, and I can update this description in the schema once I have some good words written. @gjcolombo on matrix gave some helpful descriptions of the state .

[bnaecker]

That it's empty is because we haven't done #5942 and the related work.