Add ability to customize default operating system support for new/converted modules

[scotje]

Users should be able to customize what the default operating system support is for new and newly converted modules. Currently, the pre-selected options are hard-coded.

Futher, the solution should support customizing the operating system versions that are included in the generated metadata.json.

For example, currently if you select "RedHat based Linux" in the interview process, it adds the following entry to metadata.json:

{
      "operatingsystem": "RedHat",
      "operatingsystemrelease": [
        "8"
      ]
}

It would be useful to be able to customize the contents of the operatingsystemrelease array. (For example, set it to ["5", "6", "7"] or ["6", "7", "8"].

[natemccurdy]

Big +1 to this. The hard-coded list of operating systems in https://github.com/puppetlabs/pdk/blob/v2.1.0/lib/pdk/module/metadata.rb#L8 are not always relevant to PDK users.

And in some cases this list causes spec tests failures that are red-herrings due to the OS's not being the intended target of a module.
This is my main gripe with the hard-coded list... it's not customizable.

I work with teams that are 100% CentOS shops, and they build their internal Puppet modules to only support CentOS. We use a custom PDK module template, but when doing a pdk new module, we have to hand-edit the metadata.json to remove the non-CentOS OS's.

It would be better if we could specify a default list of OS's or even make the metadata.json part of the PDK module template.