feat: Add guest execution agent and vsock support

- Introduced a standalone guest execution agent to facilitate command execution within the guest VM over Firecracker's vsock.
- Enhanced FirecrackerClient to support vsock configuration, validating guest CID and UDS path.
- Updated configuration to include vsock settings by default.
- Refactored FirecrackerProcessManager to manage runtime sockets more effectively.
- Implemented guest agent installation and provisioning in the image store.
- Added API endpoints for executing commands in the VM and installing the guest agent.
- Improved error handling for guest execution failures and agent availability.

uvm/firecracker/api.py

@@ -36,6 +36,7 @@ class FirecrackerClient:
         drives = config["drives"]
         interfaces = config["network-interfaces"]
         entropy = config.get("entropy")
+        vsock = config.get("vsock")
         if not isinstance(machine, Mapping) or not isinstance(boot, Mapping):
             raise FirecrackerError("invalid Firecracker configuration")
         if not isinstance(drives, list) or not drives:
@@ -44,6 +45,10 @@ class FirecrackerClient:
             raise FirecrackerError("Firecracker configuration has no network interface")
         if not isinstance(entropy, Mapping):
             raise FirecrackerError("Firecracker configuration has no valid entropy device")
+        if (not isinstance(vsock, Mapping) or type(vsock.get("guest_cid")) is not int
+                or not 3 <= vsock["guest_cid"] < 2**32 - 1
+                or not isinstance(vsock.get("uds_path"), str) or not vsock["uds_path"]):
+            raise FirecrackerError("Firecracker configuration has no valid vsock device")
 
         self._request(
             "PUT",
@@ -57,6 +62,7 @@ class FirecrackerClient:
         self._request("PUT", "/boot-source", boot)
         self._request("PUT", "/drives/rootfs", drives[0])
         self._request("PUT", "/network-interfaces/eth0", interfaces[0])
+        self._request("PUT", "/vsock", vsock)
         self._request("PUT", "/entropy", entropy)
         self._request("PUT", "/actions", {"action_type": "InstanceStart"})