Documentation about the `--meta` option for `imager`

[kraakevik]

Feature Request

Documentation that explains the expected format and params that the --meta option in ghcr.io/siderolabs/imager supports, especially information about custom labels baked into the image.

Description

The ghcr.io/siderolabs/imager accepts a option --imager which is documented as --meta metaValueSlice , without any further explanation.

I want to bake lables into my raw image, as Omni does when generating Installation Media, in the request I see:

meta:
    - key: 12
    - value: |
        machineLabels:
             key: value

So I figured I can set this value using the --meta option in imager. I tried a few different flavors, and managed to pass the validation, but I still can not see any labels being applied to the machine in Omni.

[kraakevik]

My last attempt actually succeeded.. the following gives me a label in Omni after machine is registered..

--meta 12='{"machineLabels": {"key":"value"}}'