Support notdefaultfor provider DSL method

Use Case

Puppet added a notdefaultfor DSL method to constrain providers, similar to defaultfor. This allows providers to default to a given osfamily, except on earlier os versions. However, strings doesn't support notdefaultfor

Describe the Solution You Would Like

Strings should emit documentation when a provider uses notdefaultfor. For example, the systemd service provider defines:

  defaultfor :operatingsystem => :debian
  notdefaultfor :operatingsystem => :debian, :operatingsystemmajrelease => ["5", "6", "7"] 

I would expect to see documentation similar to defaultfor in the docs for each provider:

<div class="tags">
  <p class="tag_title">Default Provider For</p>
  <ul>

  
    
      <li><tt>osfamily &mdash; [:archlinux]</tt></li>
    
      <li><tt>osfamily &mdash; redhat, operatingsystemmajrelease &mdash; ["7", "8"]</tt></li>
    ```
See also https://tickets.puppetlabs.com/browse/PUP-8552

Start by tracing how the provider DSL's defaultfor method is extracted and rendered in provider documentation, using the systemd service provider example as a reference. Add equivalent handling for notdefaultfor and verify that generated documentation includes the expected provider constraints.