Add worker tagging (#862)

This allows workers to have tags assigned to them, which can then be filtered to control which targets they are allowed to serve.

internal/servers/query.go

@@ -1,5 +1,18 @@
 package servers
 
 const (
-	deleteWhereSql = `create_time < $1`
+	serverUpsertQuery = `
+		insert into server
+			(private_id, type, description, address, update_time)
+		values
+			($1, $2, $3, $4, $5)
+		on conflict on constraint server_pkey
+		do update set
+			type = $2,
+			description = $3,
+			address = $4,
+			update_time = $5;
+	`
+	deleteWhereCreateTimeSql = `create_time < $1`
+	deleteTagsSql            = `server_id = $1`
 )