[AB-xxx] adding templates necessary for modmail thread support

adding validation message to enableFeature response

abstracto-modules/core/src/main/resources/en_US/commands/enableFeature/enableFeature_response_embed_en_US.ftl

@@ -1,5 +1,5 @@
 {
-    "additionalMessage": "<@safe_include "enableFeature_response_text"/>",
+    "additionalMessage": "<@safe_include "enableFeature_response_text"/><#if validationText?has_content>${validationText}</#if>",
     "messageConfig": {
         "ephemeral": true
     }

abstracto-modules/modmail/src/main/resources/en_US/command/contact/contact_response_embed_en_US.ftl

@@ -1,6 +1,3 @@
 {
-    "additionalMessage": "<@safe_include "contact_response_text"/>",
-    "messageConfig": {
-        "ephemeral": true
-    }
+    "additionalMessage": "<@safe_include "contact_response_text"/>"
 }

abstracto-modules/modmail/src/main/resources/en_US/listener/messageReceived/modmail_notification_message_embed_en_US.ftl

@@ -8,13 +8,15 @@
             },
             <#include "modmail_color">,
             <#assign user><@member_user_name member=member/>(${member.user.id})</#assign>
-            "description": "<@safe_include "modmail_notification_message_description"/>",
+            "description": "<@safe_include "modmail_notification_message_description"/>"
+            <#if channel?has_content>,
             "fields": [
                 {
                     "name": "<@safe_include "modmail_notification_field_title_channel"/>",
                     "value": "${channel.asMention}"
                 }
             ]
+            </#if>
         }
     ],
     "messageConfig": {

translations/modmail/src/main/resources/en_US/config/feature_setup_modmail_thread_container_not_setup_en_US.ftl

@@ -0,0 +1 @@
+The thread container for modmail is not correctly setup.

translations/modmail/src/main/resources/en_US/config/feature_setup_posttarget_modmailContainer_en_US.ftl

@@ -0,0 +1 @@
+The channel which should contain the modmail threads. (In the appropriate mode). This must be a channel that can contain threads. Currently: ${currentTarget}