feat: Ability to lock to single conversation (#5881)

Adds the ability to lock conversation to a single thread for Whatsapp and Sms Inboxes when using outbound messages.

demo: https://www.loom.com/share/c9e1e563c8914837a4139dfdd2503fef

fixes: #4975

Co-authored-by: Nithin David <1277421+nithindavid@users.noreply.github.com>

db/schema.rb

@@ -535,6 +535,7 @@ ActiveRecord::Schema.define(version: 2022_11_16_000514) do
     t.boolean "csat_survey_enabled", default: false
     t.boolean "allow_messages_after_resolved", default: true
     t.jsonb "auto_assignment_config", default: {}
+    t.boolean "lock_to_single_conversation", default: false, null: false
     t.index ["account_id"], name: "index_inboxes_on_account_id"
   end