Instrument ScmWebhook

To answer questions in the SCM/CI integration like:
- Which SCM is the most used?
- Which webhook event is the most frequent?

src/api/app/instrumentations/scm_webhook_instrumentation.rb

@@ -0,0 +1,29 @@
+module ScmWebhookInstrumentation
+  extend ActiveSupport::Concern
+
+  # Define callbacks with ActiveModel::Callback which is included in ActiveModel::Model
+  included do
+    define_model_callbacks :initialize
+
+    after_initialize :track_webhook
+  end
+
+  private
+
+  def track_webhook
+    RabbitmqBus.send_to_bus('metrics', "scm_webhook,scm=#{@payload[:scm]},webhook_event=#{webhook_event} count=1")
+  end
+
+  def webhook_event
+    case
+    when push_event?
+      'push'
+    when tag_push_event?
+      'tag_push'
+    when pull_request_event?
+      'pull_request'
+    else
+      'unsupported'
+    end
+  end
+end

src/api/app/models/scm_webhook.rb

@@ -1,6 +1,7 @@
 # Contains the payload extracted from a SCM webhook and provides helper methods to know which webhook event we're dealing with
 class ScmWebhook
   include ActiveModel::Model
+  include ScmWebhookInstrumentation # for run_callbacks
 
   attr_accessor :payload
 
@@ -12,9 +13,11 @@ class ScmWebhook
   IGNORED_MERGE_REQUEST_ACTIONS = ['approved', 'unapproved'].freeze
 
   def initialize(attributes = {})
-    super
-    # To safely navigate the hash and compare keys
-    @payload = attributes[:payload].deep_symbolize_keys
+    run_callbacks(:initialize) do
+      super
+      # To safely navigate the hash and compare keys
+      @payload = attributes[:payload].deep_symbolize_keys
+    end
   end
 
   def new_pull_request?