Correct config template for API transport (#8991)

Due to bug in the implementation of the alert transport mapping introduced in #8660  , the API transport is unable to be configured via the new interface. Only the 'get' method is displayed in the UI and the defined validation is expecting uppercase "GET" or "POST" as the method, making it impossible to configure the API transport.

This change corrects the name to option value mapping to uppercase GET and adds back the POST method option. 

DO NOT DELETE THIS TEXT

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LibreNMS/Alert/Transport/Api.php

@@ -87,8 +87,8 @@ class Api extends Transport
                     'descr' => 'API Method: GET or POST',
                     'type' => 'select',
                     'options' => [
-                        'get' => 'get',
-                        'get' => 'get'
+                        'GET' => 'GET',
+                        'POST' => 'POST'
                     ]
                 ],
                 [