Add information about reinstall puppet-agent-oauth

[TuningYourCode]

As i had this problem and got the answer in slack i wanted to contribute the solution to the website.

[ekohl]

In foreman-installer there's a hook that automates it:
https://github.com/theforeman/foreman-installer/blob/develop/hooks/pre/31-puppet_agent_oauth.rb
But those who use their installation directly without foreman-installer need to make sure the oauth gem is available. Either by installing puppet-agent-oauth, a manual gem install oauth in the right Ruby environment or some other way.

[TuningYourCode]

we use the foreman puppet modules to manage the foreman installation by puppet (kind of chicken & egg issue ;)) not sure how common that setup is.
If our setup is niche we can also close the PR or change the wording :) I think the case is not that important that we should do a discussion - the time is better spent on other topics.

[ekohl]

It's not that uncommon and I wanted to provide some context there are multiple ways of achieving it. In https://github.com/theforeman/puppet-foreman/blob/master/manifests/providers.pp we only support the package method, but in I think you can also use

package { 'oauth':
  ensure   => installed,
  provider => 'puppet_gem',
}