Incus has an arbitrary file write on host via `exec-output` symlink in crafted image

Incus is a system container and virtual machine manager. Prior to version 7.2.0, the `record-output` parameter of the `/instances/$name/exec` endpoint stores the output of the command in the `exec-output` directory of the instance. If `exec-output` is a symlink, file named `exec_UUID.stdout` and `exec_UUID.stderr` can be written to an arbitrary location where the `.stdout` file will contain arbitrary content. This behavior can be abused for arbitrary command execution. Version 7.2.0 contains a patch.