Refactor Ci::Pipeline's config_sources enum

This enum is now defined in the Ci::PipelineEnums module, allowing EE to
extend this enum without having to modify Ci::Pipeline directly.

app/models/ci/pipeline.rb

@@ -68,11 +68,7 @@ module Ci
     # this `Hash` with new values.
     enum_with_nil source: ::Ci::PipelineEnums.sources
 
-    enum_with_nil config_source: {
-      unknown_source: nil,
-      repository_source: 1,
-      auto_devops_source: 2
-    }
+    enum_with_nil config_source: ::Ci::PipelineEnums.config_sources
 
     # We use `Ci::PipelineEnums.failure_reasons` here so that EE can more easily
     # extend this `Hash` with new values.

app/models/ci/pipeline_enums.rb

@@ -25,5 +25,15 @@ module Ci
         merge_request: 10
       }
     end
+
+    # Returns the `Hash` to use for creating the `config_sources` enum for
+    # `Ci::Pipeline`.
+    def self.config_sources
+      {
+        unknown_source: nil,
+        repository_source: 1,
+        auto_devops_source: 2
+      }
+    end
   end
 end