archetypes: create an agent from an archetype with no config repo

POST /api/agents takes an archetype the stored list holds, records it in
the new agent-archetype bucket, and queues no CreateRepo, AddRepoMember or
InitAgentConfigRepo for it. A destroy clears the key. Hives may read the
bucket.

Refs #5386

swarm-controller/src/agent_permissions.rs

@@ -797,6 +797,7 @@ mod tests {
                     limits: None,
                     inference: None,
                     permissions,
+                    archetype: None,
                 }),
             )
         };
@@ -857,6 +858,7 @@ mod tests {
                 limits: None,
                 inference: None,
                 permissions: None,
+                archetype: None,
             }),
         )
         .await