Find a better place for the PipelineExecutionPolicy class/struct

Summary

In !158198 (merged) and !151339 (merged), we decided to have a "carrier" class/struct for pipeline execution policies that will store the created pipeline and some attributes of the policy.

For now, we added this into ee/lib/ee/gitlab/ci/pipeline/chain/pipeline_execution_policies/find_configs.rb but maybe there is a better way to handle this. We also use it in ee/spec/factories/ci/pipeline_execution_policy.rb.

PipelineExecutionPolicy = Struct.new(:pipeline, :strategy) do
  def strategy_override_project_ci?
    strategy == :override_project_ci
  end
end

Implementation plan

We can move the struct into the Gitlab::Ci::Pipeline::Chain namespace to its own class. This would match the pattern we already use with Gitlab::Ci::Pipeline::Chain::Command

diff --git a/ee/lib/ee/gitlab/ci/pipeline/chain/pipeline_execution_policies/find_configs.rb b/ee/lib/ee/gitlab/ci/pipeline/chain/pipeline_execution_policies/find_configs.rb
index 31b10d7d3adb..bdf684294c80 100644
--- a/ee/lib/ee/gitlab/ci/pipeline/chain/pipeline_execution_policies/find_configs.rb
+++ b/ee/lib/ee/gitlab/ci/pipeline/chain/pipeline_execution_policies/find_configs.rb
@@ -24,12 +24,6 @@ module FindConfigs
               include ::Gitlab::Utils::StrongMemoize
               extend ::Gitlab::Utils::Override
 
-              PipelineExecutionPolicy = Struct.new(:pipeline, :strategy) do
-                def strategy_override_project_ci?
-                  strategy == :override_project_ci
-                end
-              end
-
               override :perform!
               def perform!
                 return if ::Feature.disabled?(:pipeline_execution_policy_type, project.group)
@@ -43,7 +37,7 @@ def perform!
                   pipeline = response.payload
 
                   if response.success?
-                    command.pipeline_execution_policies << PipelineExecutionPolicy.new(pipeline, config.strategy)
+                    command.pipeline_execution_policies << ::Gitlab::Ci::Pipeline::Chain::PipelineExecutionPolicy.new(pipeline, config.strategy)
                   elsif pipeline.filtered_as_empty?
                     # no-op: we ignore empty pipelines
                   else
diff --git a/ee/spec/factories/ci/pipeline_execution_policy.rb b/ee/spec/factories/ci/pipeline_execution_policy.rb
index c237053d152c..d623cc6a7fb5 100644
--- a/ee/spec/factories/ci/pipeline_execution_policy.rb
+++ b/ee/spec/factories/ci/pipeline_execution_policy.rb
@@ -3,7 +3,7 @@
 FactoryBot.define do
   factory(
     :ci_pipeline_execution_policy,
-    class: '::Gitlab::Ci::Pipeline::Chain::PipelineExecutionPolicies::FindConfigs::PipelineExecutionPolicy'
+    class: '::Gitlab::Ci::Pipeline::Chain::PipelineExecutionPolicy'
   ) do
     pipeline factory: :ci_empty_pipeline
     strategy { :inject_ci }