Add 10s and 15s buckets to step histogram

p99 of pipeline creation is generally between 5s and 20s, so adding
additional buckets between that will give us needed insight into step
creation duration.

lib/gitlab/ci/pipeline/metrics.rb

@@ -18,7 +18,7 @@ module Gitlab
           description = step.gsub('gitlab_ci_', '').tr('_', ' ')
           comment = "Duration of the #{description}"
           labels = {}
-          buckets = [0.01, 0.05, 0.1, 0.5, 1.0, 2.0, 5.0, 20.0, 50.0, 240.0]
+          buckets = [0.01, 0.05, 0.1, 0.5, 1.0, 2.0, 5.0, 10.0, 15.0, 20.0, 50.0, 240.0]
 
           ::Gitlab::Metrics.histogram(name, comment, labels, buckets)
         end

spec/lib/gitlab/ci/pipeline/metrics_spec.rb

@@ -12,7 +12,7 @@ RSpec.describe ::Gitlab::Ci::Pipeline::Metrics do
           :gitlab_ci_pipeline_chain_build_duration_seconds,
           'Duration of the pipeline chain build',
           {},
-          [0.01, 0.05, 0.1, 0.5, 1.0, 2.0, 5.0, 20.0, 50.0, 240.0]
+          [0.01, 0.05, 0.1, 0.5, 1.0, 2.0, 5.0, 10.0, 15.0, 20.0, 50.0, 240.0]
         )
 
       described_class.pipeline_creation_step_duration_histogram(step)