Exclude non-discoverable silos from IP pool silos list

[david-crespo]

They're still linkable, just like they're still GETable by name or ID. They just don't show up in lists.

Closes #4955

[david-crespo]

Matching the logic in silos_list. Since we're not joining on silo, we can also filter out links to deleted silos, even though it should be impossible to have any such links after #4867.

omicron/nexus/db-queries/src/db/datastore/silo.rs

Lines 322 to 351 in 0531d61

	pub async fn silos_list(
	&self,
	opctx: &OpContext,
	pagparams: &PaginatedBy<'_>,
	discoverability: Discoverability,
	) -> ListResultVec<Silo> {
	opctx.authorize(authz::Action::ListChildren, &authz::FLEET).await?;
	use db::schema::silo::dsl;
	let mut query = match pagparams {
	PaginatedBy::Id(params) => paginated(dsl::silo, dsl::id, &params),
	PaginatedBy::Name(params) => paginated(
	dsl::silo,
	dsl::name,
	&params.map_name(|n| Name::ref_cast(n)),
	),
	}
	.filter(dsl::id.ne(INTERNAL_SILO.id()))
	.filter(dsl::time_deleted.is_null());
	if let Discoverability::DiscoverableOnly = discoverability {
	query = query.filter(dsl::discoverable.eq(true));
	}
	query
	.select(Silo::as_select())
	.load_async::<Silo>(&*self.pool_connection_authorized(opctx).await?)
	.await
	.map_err(|e| public_error_from_diesel(e, ErrorHandler::Server))
	}

[david-crespo]

Leaning toward not adding this additional filter. The goal is to convert existing data to the new model while keeping the logic the same, and if P0 is a fleet default pool before this migration, it is accessible from non-discoverable silos. So in order to keep the behavior the same after the migration, P0 should be linked to those silos.