Parameterise params class for '$php_conf_dir'

[grant-veepshosting]

Given PHPv5 is end-of-life, end-of-support, we can more effectively cater to supported versions by moving the 'Debian' OS default to an override-able parameter. eg.

class newrelic::params (
  Optional[String] $php_config_dir = '/etc/php/7.4/mods-available',
){
... (unchanged most of the code)...
    'Debian': {
      $manage_repo                 = true
      $server_package_name         = 'newrelic-sysmond'
      $server_service_name         = 'newrelic-sysmond'
      $php_package_name            = 'newrelic-php5'
      $php_service_name            = 'newrelic-daemon'
      $php_default_ini_settings    = {}
      $php_default_daemon_settings = {}
      $php_extra_packages          = []
      $run_installer               = false

      case $facts['os']['distro']['codename'] {
        'xenial','stretch': { $php_conf_dir = '/etc/php/7.0/mods-available' }
        default:            { $php_conf_dir = $php_config_dir }
      }
    }