Rename source to pipeline_source in the pipeline logger

We already have a source and it's overriding this key in the logged
data.

lib/gitlab/ci/pipeline/logger.rb

@@ -51,7 +51,7 @@ module Gitlab
             project_id: project.id,
             pipeline_id: pipeline.id,
             persisted: pipeline.persisted?,
-            source: pipeline.source,
+            pipeline_source: pipeline.source,
             duration_s: age
           }.stringify_keys.merge(observations_hash)
 

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

@@ -76,7 +76,7 @@ RSpec.describe ::Gitlab::Ci::Pipeline::Logger do
           'project_id' => project.id,
           'duration_s' => a_kind_of(Numeric),
           'caller' => 'source',
-          'source' => pipeline.source,
+          'pipeline_source' => pipeline.source,
           'pipeline_save_duration_s' => {
             'avg' => 60, 'count' => 1, 'max' => 60, 'min' => 60
           },

spec/services/ci/create_pipeline_service/logger_spec.rb

@@ -28,7 +28,7 @@ RSpec.describe Ci::CreatePipelineService do
     let(:loggable_data) do
       {
         'caller' => 'Ci::CreatePipelineService',
-        'source' => 'push',
+        'pipeline_source' => 'push',
         'pipeline_id' => a_kind_of(Numeric),
         'persisted' => true,
         'project_id' => project.id,
@@ -80,7 +80,7 @@ RSpec.describe Ci::CreatePipelineService do
         let(:loggable_data) do
           {
             'caller' => 'Ci::CreatePipelineService',
-            'source' => 'push',
+            'pipeline_source' => 'push',
             'pipeline_id' => nil,
             'persisted' => false,
             'project_id' => project.id,