Feature Request: Allow setting HCLOUD_CLUSTER_CONFIG_FILE to point to a config file

[hegerdes]

Which component are you using?:
cluster-autoscaler

Is your feature request designed to solve a problem? If so describe the problem this feature should solve.:

Currently the way to configure the hetzner provider is via HCLOUD_CLUSTER_CONFIG. This is a json document which may contain a stingified cloud-init and other properties, so it can become quite large. While the max Linux env size is 128kb, so it should fit quite some content is is impracticable to to handle HCLOUD_CLUSTER_CONFIG via the console with all the escaping and encoding. It also does not allow refreshes of the value without a container restart.

Describe the solution you'd like.:
Similar to hcloud-ccm allow to set HCLOUD_CLUSTER_CONFIG_FILE which points to a config file. This would also allow using the downwardAPI which would allow live refreshes of the files content.

Describe any alternative solutions you've considered.:
Keep using the env solution.

Additional context.:
Having base64 encoded json which contains a stingified cloud-init yaml/json is a not so nice format to work with, even worse if you put it in a secret since now it is double base64ed. Having a file would make debugging and getting the format right a lot easier since you can edit it and dont have to replace the entire env.

[hegerdes]

If this is a welcomed feature I would be happy for trying to provide an implementation.

/area cluster-autoscaler
/area provider/hetzner