Automatically call the Garden Linux release page workflow from GLCI after successful publishing

[MrBatschner]

What would you like to be added:

Once glci successfully published Garden Linux to the cloud providers, it should automatically issue a workflow dispatch event (ref) to the release page GH Action workflow.

Why is this needed:

It should not be necessary to manually run the release page generator.

[fwilhe]

• Update the release process docs once this is done (maybe automated steps should still be described somewhere but it needs to be clear that they don't need to be run manually)