Add defined type for telegraf::processor to define processors

[philomory]

Pull Request (PR) description

This PR simply adds a telegraf::processor defined type which is analogous to the telegraf::input and telegraf::output defined types. You can use it to e.g. define a regex processor:

telegraf::processor { 'regex':
  options => [
    {
      namepass => ['nginx_requests'],
      tags     => [
        {
          key         => 'resp_code',
          pattern     => String(/^(\d)\d\d$/),
          replacement => '${1}xx',
        }
      ],
      fields   => [
        {
          key         => 'request',
          pattern     => String(/^/api(?P<method>/[\w/]+)\S*/),
          replacement => '${method}',
          result_key  => 'method',
        },
        {
          key         => 'request',
          pattern     => String(/.*category=(\w+).*/),
          replacement => '${1}',
          result_key  => 'search_category',
        },
      ],
    },
  ],
}

[dhoppe]

@philomory Thank you very much for your contribution. Could you please add some tests, update the docs and do the same for aggregators? This would be awesome.

[philomory]

@dhoppe I made the requested additions, let me know what you think.