search: log extra search metadata to NewRelic.

When a user does a tag search, log a few more things, including the normalized
search string, the number of tags in the search string, and the number of results.

app/controllers/posts_controller.rb

@@ -12,6 +12,7 @@ class PostsController < ApplicationController
       tag_query = params[:tags] || params.dig(:post, :tags)
       @post_set = PostSets::Post.new(tag_query, params[:page], params[:limit], random: params[:random], format: params[:format])
       @posts = authorize @post_set.posts, policy_class: PostPolicy
+      @post_set.log!
       respond_with(@posts) do |format|
         format.atom
       end