Track wiki page views in usage data

This adds a new `view` event in `WikiPageCounter` and increases it every
time a wiki page is rendered.

app/controllers/concerns/wiki_actions.rb

@@ -67,6 +67,8 @@ module WikiActions
       @ref = params[:version_id]
       @path = page.path
 
+      Gitlab::UsageDataCounters::WikiPageCounter.count(:view)
+
       render 'shared/wikis/show'
     elsif file_blob
       send_blob(wiki.repository, file_blob)

changelogs/unreleased/218161-wiki-page-views-usage-ping.yml

+---
+title: Track wiki page views in usage data
+merge_request: 38784
+author:
+type: changed

doc/development/telemetry/event_dictionary.md

@@ -230,9 +230,10 @@ An event dictionary is a single source of truth that outlines what events and pr
 | `merge_requests`                                          | `counts`                             |               |                  |         |                                                                            |
 | `merge_requests_users`                                    | `counts`                             |               |                  |         |                                                                            |
 | `notes`                                                   | `counts`                             |               |                  |         |                                                                            |
-| `wiki_pages_create`                                       | `counts`                             |               |                  |         |                                                                            |
-| `wiki_pages_update`                                       | `counts`                             |               |                  |         |                                                                            |
-| `wiki_pages_delete`                                       | `counts`                             |               |                  |         |                                                                            |
+| `wiki_pages_view`                                         | `counts`                             | `create`      |                  | CE+EE   | Number of viewed wiki pages                                                |
+| `wiki_pages_create`                                       | `counts`                             | `create`      |                  | CE+EE   | Number of created wiki pages                                               |
+| `wiki_pages_update`                                       | `counts`                             | `create`      |                  | CE+EE   | Number of updated wiki pages                                               |
+| `wiki_pages_delete`                                       | `counts`                             | `create`      |                  | CE+EE   | Number of deleted wiki pages                                               |
 | `web_ide_commits`                                         | `counts`                             |               |                  |         |                                                                            |
 | `web_ide_views`                                           | `counts`                             |               |                  |         |                                                                            |
 | `web_ide_merge_requests`                                  | `counts`                             |               |                  |         |                                                                            |

lib/gitlab/usage_data_counters/wiki_page_counter.rb

@@ -2,7 +2,7 @@
 
 module Gitlab::UsageDataCounters
   class WikiPageCounter < BaseCounter
-    KNOWN_EVENTS = %w[create update delete].freeze
+    KNOWN_EVENTS = %w[view create update delete].freeze
     PREFIX = 'wiki_pages'
   end
 end

spec/lib/gitlab/usage_data_counters/wiki_page_counter_spec.rb

@@ -3,11 +3,13 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::UsageDataCounters::WikiPageCounter do
+  it_behaves_like 'a redis usage counter', 'Wiki Page', :view
   it_behaves_like 'a redis usage counter', 'Wiki Page', :create
   it_behaves_like 'a redis usage counter', 'Wiki Page', :update
   it_behaves_like 'a redis usage counter', 'Wiki Page', :delete
 
   it_behaves_like 'a redis usage counter with totals', :wiki_pages,
+    view: 8,
     create: 5,
     update: 3,
     delete: 2

spec/support/shared_examples/controllers/wiki_actions_shared_examples.rb

@@ -161,6 +161,14 @@ RSpec.shared_examples 'wiki controller actions' do
         expect(assigns(:sidebar_limited)).to be(false)
       end
 
+      it 'increases the page view counter' do
+        expect do
+          subject
+
+          expect(response).to have_gitlab_http_status(:ok)
+        end.to change { Gitlab::UsageDataCounters::WikiPageCounter.read(:view) }.by(1)
+      end
+
       context 'when page content encoding is invalid' do
         it 'sets flash error' do
           allow(controller).to receive(:valid_encoding?).and_return(false)