feat(Beaker): Support custom configurable ks_meta values

[Tiboris]

get the ks_meta from host configuration, global provisioning config or default hardcoded in code. The priority is following:

• host
• provisioning-config.yaml
• default (if nothing set) https://beaker-project.org/docs/user-guide/customizing-installation.html#kickstart-metadata-ks-meta

[pvoborni]

Approved. It works. Looks OK. But have a Q: Why is one key named ks_meta and the other kickstart_metadata shouldn't it be the same, or is there some other specific reason?

[Tiboris]

To reply to above comment the reason is just that it is more readable in my opinion ks_meta is variable passed to provider which is supported to it but it is basically kickstart_metadata which user can pass as a string. If that's not what we want we can rename it to ks_meta of course.

[pvoborni]

We can merge this. My only worry is that it will confuse users. Time will tell.