implemented contact command and added check if the thread already exists

added anon reply command

abstracto-application/abstracto-modules/modmail/modmail-impl/src/main/resources/templates/command/contact/modmail_thread_already_exists_embed_en_US.ftl

@@ -0,0 +1,18 @@
+{
+  "author": {
+    "name": "${member.effectiveName}",
+    "avatar":  "${member.user.effectiveAvatarUrl}"
+  },
+  "color" : {
+    "r": 200,
+    "g": 0,
+    "b": 255
+  },
+  "description": "<#include "modmail_thread_already_exists">",
+  "fields": [
+     {
+        "name": "<#include "modmail_existing_thread_link_field_title">",
+        "value": "[<#include "modmail_existing_thread_link_content_display_text">](${threadUrl})"
+     }
+  ]
+}