feat: Draft through API for Cross-Device Support (#8018)

- Add APIs for cross-device message drafts

ref: #6890

app/controllers/api/v1/accounts/conversations/draft_messages_controller.rb

@@ -0,0 +1,28 @@
+class Api::V1::Accounts::Conversations::DraftMessagesController < Api::V1::Accounts::Conversations::BaseController
+  def show
+    render json: { has_draft: false } and return unless Redis::Alfred.exists?(draft_redis_key)
+
+    draft_message = Redis::Alfred.get(draft_redis_key)
+    render json: { has_draft: true, message: draft_message }
+  end
+
+  def update
+    Redis::Alfred.set(draft_redis_key, draft_message_params)
+    head :ok
+  end
+
+  def destroy
+    Redis::Alfred.delete(draft_redis_key)
+    head :ok
+  end
+
+  private
+
+  def draft_redis_key
+    format(Redis::Alfred::CONVERSATION_DRAFT_MESSAGE, id: @conversation.id)
+  end
+
+  def draft_message_params
+    params.dig(:draft_message, :message) || ''
+  end
+end