Draft: Optimize pipelines serializer

What does this MR do and why?

The purpose of this MR is to optimize pipelines serializer, more specifically the performance of requests to Projects::MergeRequestsController#pipelines.json.

The proposed solution in the issue was to find a not to query stages.action when it is not needed (the pipeline list views).

• Both the Projects::MergeRequestsController#pipelines and Projects::Pipeline#index actions currently pass a param to the serializer set to true - disable_manual_and_scheduled_actions: true
• This param is used to bypass loading and exposing manual_actions and scheduled_actions in PipelineDetailsEntity
• it was added in this MR to try and resolve a similar issue

The changes in this MR leverage the existing param to further bypass loading actions when they are not required

• add a conditional to DetailedStatusEntity to not expose action if disable_manual_and_scheduled_actions is true
• bypass preloading manual and scheduled actions in the PipelineSerializer if disable_manual_and_scheduled_actions is true

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Related to #525559 (closed)