feat: Line Channel (#2904)

- Ability to configure line bots as a channel in chatwoot
- Receive a message sent to the line bot in chatwoot
- Ability to reply to line users from chatwoot

fixes: #2738

db/migrate/20210829124254_add_line_channel.rb

@@ -0,0 +1,11 @@
+class AddLineChannel < ActiveRecord::Migration[6.1]
+  def change
+    create_table :channel_line do |t|
+      t.integer :account_id, null: false
+      t.string :line_channel_id, null: false, index: { unique: true }
+      t.string :line_channel_secret, null: false
+      t.string :line_channel_token, null: false
+      t.timestamps
+    end
+  end
+end