uploads: add /upload_media_assets index page.

This page shows each individual file you've uploaded. This is different
from the regular uploads page because files in multi-file uploads are
not grouped together.

app/controllers/upload_media_assets_controller.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class UploadMediaAssetsController < ApplicationController
+  respond_to :html, :xml, :json, :js
+
+  def index
+    @upload_media_assets = authorize UploadMediaAsset.visible(CurrentUser.user).includes(media_asset: :post, upload: :uploader).where(upload: { uploader: CurrentUser.user }).paginated_search(params, count_pages: true)
+    respond_with(@upload_media_assets)
+  end
+
+  def show
+    @upload_media_asset = authorize UploadMediaAsset.find(params[:id])
+    @media_asset = @upload_media_asset.media_asset
+
+    if request.format.html? && @media_asset&.post&.present?
+      flash[:notice] = "Duplicate of post ##{@media_asset.post.id}"
+      redirect_to @media_asset.post
+    else
+      respond_with(@upload_media_asset)
+    end
+  end
+end