fix(docker): handle container name conflict automatically

When a Docker container with the same name already exists (e.g., from a
   previous crashed GNS3 session), Docker returns a 409 Conflict error
   when trying to create a new container with that name. This causes the
   project open operation to fail.

   This fix adds automatic cleanup of stale containers when encountering
   a name conflict:
   - Added DockerHttp409Error exception class
   - Updated http_query to detect 409 status codes
   - Modified create() to remove conflicting containers and retry

   Fixes the issue where opening a project fails with:
   "Docker has returned an error: 409 Conflict. The container name
   '/GNS3.xxx' is already in use by container 'xxx'"

gns3server/compute/docker/__init__.py

@@ -32,7 +32,7 @@ from gns3server.config import Config
 from gns3server.utils.asyncio import locking
 from gns3server.compute.base_manager import BaseManager
 from gns3server.compute.docker.docker_vm import DockerVM
-from gns3server.compute.docker.docker_error import DockerError, DockerHttp304Error, DockerHttp404Error
+from gns3server.compute.docker.docker_error import DockerError, DockerHttp304Error, DockerHttp404Error, DockerHttp409Error
 
 log = logging.getLogger(__name__)
 
@@ -240,6 +240,8 @@ class Docker(BaseManager):
                 raise DockerHttp304Error(f"Docker has returned an error: {response.status} {body}")
             elif response.status == 404:
                 raise DockerHttp404Error(f"Docker has returned an error: {response.status} {body}")
+            elif response.status == 409:
+                raise DockerHttp409Error(f"Docker has returned an error: {response.status} {body}")
             else:
                 raise DockerError(f"Docker has returned an error: {response.status} {body}")
         return response