fix(mainWindow/conversation): use placeholder on textarea

tests/languages/en.ts

@@ -48,6 +48,10 @@
         <source>displayMessages</source>
         <translation>Messages</translation>
     </message>
+    <message>
+        <source>newMessagePlaceholder</source>
+        <translation>Enter your message</translation>
+    </message>
 </context>
 <context>
     <name>home</name>

tests/languages/fr.ts

@@ -48,6 +48,10 @@
         <source>displayMessages</source>
         <translation>Messages</translation>
     </message>
+    <message>
+        <source>newMessagePlaceholder</source>
+        <translation>Entrer votre message.</translation>
+    </message>
 </context>
 <context>
     <name>home</name>

tests/ui/views/mainWindow/conversation.qml

@@ -147,6 +147,7 @@ ColumnLayout  {
                 ScrollBar.vertical: ScrollBar { }
                 TextArea.flickable: TextArea {
                     id: textArea
+                    placeholderText: qsTr('newMessagePlaceholder')
                     wrapMode: TextArea.Wrap
                 }
             }