fix: Set avatar for users(agent/contact) in slack channels (#7960)

app/controllers/slack_uploads_controller.rb

@@ -0,0 +1,27 @@
+class SlackUploadsController < ApplicationController
+  include Rails.application.routes.url_helpers
+  before_action :set_blob, only: [:show]
+
+  def show
+    if @blob
+      redirect_to blob_url
+    else
+      redirect_to avatar_url
+    end
+  end
+
+  private
+
+  def set_blob
+    @blob = ActiveStorage::Blob.find_by(key: params[:blob_key])
+  end
+
+  def blob_url
+    url_for(@blob.representation(resize_to_fill: [250, nil]))
+  end
+
+  def avatar_url
+    base_url = ENV.fetch('FRONTEND_URL', nil)
+    "#{base_url}/integrations/slack/#{params[:sender_type]}.png"
+  end
+end