feat: outbound voice call essentials (#12782)

- Enables outbound voice calls in voice channel . We are only caring
about wiring the logic to trigger outgoing calls to the call button
introduced in previous PRs. We will connect it to call component in
subsequent PRs

ref: #11602 

## Screens

<img width="2304" height="1202" alt="image"
src="https://github.com/user-attachments/assets/b91543a8-8d4e-4229-bd80-9727b42c7b0f"
/>

<img width="2304" height="1200" alt="image"
src="https://github.com/user-attachments/assets/1a1dad2a-8cb2-4aa2-9702-c062416556a7"
/>

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Vishnu Narayanan <vishnu@chatwoot.com>

enterprise/app/builders/enterprise/contact_inbox_builder.rb

@@ -0,0 +1,21 @@
+module Enterprise::ContactInboxBuilder
+  private
+
+  def generate_source_id
+    return super unless @inbox.channel_type == 'Channel::Voice'
+
+    phone_source_id
+  end
+
+  def phone_source_id
+    return super unless @inbox.channel_type == 'Channel::Voice'
+
+    return SecureRandom.uuid if @contact.phone_number.blank?
+
+    @contact.phone_number
+  end
+
+  def allowed_channels?
+    super || @inbox.channel_type == 'Channel::Voice'
+  end
+end

enterprise/app/builders/enterprise/messages/message_builder.rb

@@ -0,0 +1,9 @@
+module Enterprise::Messages::MessageBuilder
+  private
+
+  def message_type
+    return @message_type if @message_type == 'incoming' && @conversation.inbox.channel_type == 'Channel::Voice'
+
+    super
+  end
+end