Fix PipelineController#index N+1

What does this MR do?

Related to #321788

Fixes an N+1 in the PipelineDetailsEntity (rendered from PipelineController#index) where build metadata was queried for every build in the result set.

Done by preloading metadata for manual_actions and scheduled_actions. We were already doing this for failed_builds, but not for these two. I'm not 100% sure if there are others I am not catching here.

Before:

1) PipelineSerializer#represent number of queries when preloaded with scheduled and manual builds sends at most one metadata query for each type of build
     Failure/Error: expect(count_queries_matching(run, "SELECT \"ci_builds_metadata\".*")).to eq(1 + 2)
     
       expected: 3
            got: 5

After:

sends at most one metadata query for each type of build

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1 example, 0 failures

i.e. this will reduce query count from build_types_queried * num_builds_of_this_type to just build_types_queried * 1. The gain of this will largely depend on how many builds there are of types scheduled or manual.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
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• Style guides
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• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done