feat: Ability to lock the conversation to a single thread in API channels (#10329)

Added the possibility to mark as a single conversation in the API type
inbox. This allows the conversation builder to search for the last
conversation.
I thought about searching for the last conversation with created_at:
desc order, as is done in some channels... but I didn't change the way
the conversation is searched.

Fixes: #7726 

Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/javascript/dashboard/routes/dashboard/settings/inbox/Settings.vue

@@ -175,7 +175,10 @@ export default {
     },
     canLocktoSingleConversation() {
       return (
-        this.isASmsInbox || this.isAWhatsAppChannel || this.isAFacebookInbox
+        this.isASmsInbox ||
+        this.isAWhatsAppChannel ||
+        this.isAFacebookInbox ||
+        this.isAPIInbox
       );
     },
     inboxNameLabel() {