Add ticket reply API endpoints

GET /api/v1/ticket_replies/read.php and POST create.php, so an RMM or
monitoring system can append to a ticket it did not open.

Replies default to Internal so an integration cannot email a client by
omitting a parameter. Public replies mark first response, notify the
contact and watchers, and fire the same custom actions as the agent
reply handler. An optional ticket_status also sets the status, and
resolves the ticket and marks the resolution SLA when set to 4.

Replies are always joined to tickets so ticket_client_id is checked
against the key user's client scope, and the client_id named on a write
must match the ticket's own client. The reply is attributed to the user
the API key runs as.

read.php resolves ticket_reply_by_name, since that column holds a
user_id on Internal and Public replies but a contact_id on Client ones.

api/v1/enforce_api_rbac.php

@@ -124,6 +124,7 @@ $resource_module = [
     'networks'      => 'module_support',
     'software'      => 'module_support',
     'tickets'       => 'module_support',
+    'ticket_replies' => 'module_support',
     'technicians'   => 'module_support',
     'clients'       => 'module_client',
     'contacts'      => 'module_client',