CLI docs: cloud-init devel hotplug-hook <subcommand> --help is empty or lacks mention of required --subsystem param.

# Bug report
No parameter information about the required --subsystem option is provided by `cloud-init devel hotplug-hook query --help` or `handle --help`

```
root@test-n:~# cloud-init devel hotplug-hook query -h
usage: /usr/bin/cloud-init devel hotplug-hook query [-h]

options:
-h, --help show this help message and exit

root@test-n:~# cloud-init devel hotplug-hook handle --help
usage: /usr/bin/cloud-init devel hotplug-hook handle [-h] -d PATH -u {add,remove}

options:
-h, --help show this help message and exit
-d PATH, --devpath PATH
Sysfs path to hotplugged device
-u {add,remove}, --udevaction {add,remove}
Specify action to take.
```
Expected representation of the required --subsystem parameter in both cases.

Affects cloud-init 21b2b6e4423b0fec325b32042c05ef4274cdd301 and earlier