Exclude child pipelines from tag and branch query

What does this MR do and why?

Exclude child pipelines from tag and branch query

When we search pipelines, we exclude child pipelines by default, however when we scope the query by branch or tag we return the last child pipeline instead of the parent one.

This change is behind a feature flag called exclude_child_pipelines_from_tag_branch_query. Rollout issue: #463296.

Changelog: fixed

Closes gitlab-com/gl-infra/delivery#20034

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