Default webhook type to github

Prior to this commit, providing the webhook type was required.

After this commit, the webhook type will default to github since
that should serve the majority of users.  This type covers gitlab
and github so that means bitbucket users will need to change it.

Author: npwalker

manifests/code_manager.pp

@@ -3,7 +3,7 @@
   $code_manager_service_user          = 'code_manager_service_user',
   $token_directory                    = '/etc/puppetlabs/puppetserver/.puppetlabs',
   $gms_api_token                      = hiera('gms_api_token', undef),
-  $git_management_system              = hiera('git_management_system', undef),
+  $git_management_system              = hiera('git_management_system', 'github'),
   $code_manager_ssh_key_directory     = '/etc/puppetlabs/puppetserver/ssh',
   $code_manager_ssh_key_file_name     = 'id-control_repo.rsa',
   $code_manager_role_name             = 'Deploy Environments',