openapi: Add missing BreakPoint variant to VmState

The VmState enum in vmm/src/vm.rs has five variants (Created,
Running, Shutdown, Paused, BreakPoint) but the OpenAPI document
only lists four. BreakPoint is observable through vm.info when a
guest_debug build is paused by the GDB stub (Vm::debug_pause).

Clients generated with strict enum handling (e.g. via
openapi-generator) fail to deserialize the vm.info response in
that state. The document already covers guest_debug-gated surface
such as /vm.coredump, so the enum should be complete as well.

Signed-off-by: leo03164 <leo03164@gmail.com>

vmm/src/api/openapi/cloud-hypervisor.yaml

@@ -582,7 +582,7 @@ components:
 
     VmState:
       type: string
-      enum: [Created, Running, Shutdown, Paused]
+      enum: [Created, Running, Shutdown, Paused, BreakPoint]
 
     VmInfo:
       required: