Add support for probing process count

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-monitor (0.0.9)
+    gitlab-monitor (0.0.10)
       pg (~> 0.18.4)
       quantile (~> 0.2.0)
       redis-namespace (~> 1.5.2)

config/gitlab-monitor.yml.example

@@ -21,6 +21,7 @@ probes:
     methods:
       - probe_memory
       - probe_age
+      - probe_count
     opts:
       - pid_or_pattern: "sidekiq .* \\[.*?\\]"
         name: sidekiq

lib/gitlab_monitor/cli.rb

@@ -322,6 +322,7 @@ module GitLab
           ::GitLab::Monitor::ProcessProber.new(pid_or_pattern: @pid || @pattern, name: @name, quantiles: @quantiles)
                                           .probe_memory
                                           .probe_age
+                                          .probe_count
                                           .write_to(@target)
         end
       end

lib/gitlab_monitor/process.rb

@@ -104,6 +104,12 @@ module GitLab
         self
       end
 
+      def probe_count
+        @metrics.add("process_count", @pids.count, name: @name.downcase)
+
+        self
+      end
+
       def write_to(target)
         target.write(@metrics.to_s)
       end

lib/gitlab_monitor/version.rb

 module GitLab
   module Monitor
-    VERSION = "0.0.9".freeze
+    VERSION = "0.0.10".freeze
   end
 end