Update piplines created metric name

* Use `_total` naming convention.
* Add to metrics documentation.

app/services/ci/create_pipeline_service.rb

@@ -135,7 +135,7 @@ module Ci
     end
 
     def pipeline_created_counter
-      @pipeline_created_counter ||= Gitlab::Metrics.counter(:pipelines_created_count, "Pipelines created count")
+      @pipeline_created_counter ||= Gitlab::Metrics.counter(:pipelines_created_total, "Counter of pipelines created")
     end
   end
 end

doc/administration/monitoring/prometheus/gitlab_metrics.md

@@ -39,6 +39,7 @@ In this experimental phase, only a few metrics are available:
 | filesystem_readable               | Gauge     | Whether or not the filesystem is readable |
 | http_requests_total               | Counter   | Rack request count |
 | http_request_duration_seconds     | Histogram | HTTP response time from rack middleware |
+| pipelines_created_total           | Counter   | Counter of pipelines created |
 | rack_uncaught_errors_total        | Counter   | Rack connections handling uncaught errors count |
 | redis_ping_timeout                | Gauge     | Whether or not the last redis ping timed out |
 | redis_ping_success                | Gauge     | Whether or not the last redis ping succeeded |

spec/services/ci/create_pipeline_service_spec.rb

@@ -40,7 +40,7 @@ describe Ci::CreatePipelineService, :services do
 
       it 'increments the prometheus counter' do
         expect(Gitlab::Metrics).to receive(:counter)
-          .with(:pipelines_created_count, "Pipelines created count")
+          .with(:pipelines_created_total, "Counter of pipelines created")
           .and_call_original
 
         pipeline