Convert to PDK v3.0.0 and add support for Puppet 8

[Phil-Friderici]

This PR will convert the module to utilize PDK v3.0.0.

• refactored the code to follow the style guides from puppet-lint and rubocop
• added support for Puppet 8
• fix minor details
• add more complete unit tests
• add Github actions for automatic code validation and unit testing [1]

Fixes #51
Fixes #75

[1] until merged, you can see the results in the PR my fork Phil-Friderici#3

[dvdme]

Can this be merged as soon as possible? Current version available form puppet module install does not work with Puppet 8.

[jackdpeterson]

@thias -- is this project still active? I'm upgrading to puppet 8 and I see this PR probably resolves issues I'm running into:

Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Unknown variable: '::osfamily'. (file: /home/ubuntu/configs/puppet/modules/sysctl/manifests/params.pp, line: 4, column: 7)