[nexus] Deprecate rack-specific "tuf_base_url" (it's no longer used)

[smklein]

Context: #1239 (comment)

Consideration: when we have a multi-rack deployment, what scope do we want "updates URL" to apply to?
If the answer is "at a whole region / AZ level", this information could be moved to a global scope, to avoid conflating the metadata with individual racks.

[bnaecker]

@smklein Is this still an issue? The relevant line of code here:

omicron/nexus/src/app/update.rs

Lines 29 to 32 in 4e64efa

	let _updates_config =
	self.updates_config.as_ref().ok_or_else(|| {
	Error::internal_error("updates system not initialized")
	})?;

appears to not use the updates_config object at all anymore. I gather from the XXX there that we still have work to do, but I'm unfamiliar with this bit of code.

[smklein]

I think this is still relevant - in omicron/nexus/db-model/src/rack.rs, tuf_base_url is still hanging off the Rack object, and I think that's the URL we should consider moving "up one layer".

E.g., should a cluster be in agreement about the TUF repo being referenced? Would it be a problem if multiple racks referenced different TUF repos?

[davepacheco]

Is that URL used for anything? It feels like the target system release (which exists now as a separate thing in the database that's broader than the rack) is the thing that represents this now.

[smklein]

Is that URL used for anything? It feels like the target system release (which exists now as a separate thing in the database that's broader than the rack) is the thing that represents this now.

Great point, I only see it used in omdb, (it does look ancient, and seems fully replaced). Maybe we can deprecate it instead?