Edits to use 'merged results' for consistency

What does this MR do and why?

This merge request changes merged result pipeline to merged results pipeline for consistency - this change aligns with the name used in the merge request settings. Additionally, there are minor tweaks to the documentation for merge train pipelines, including replacing able with cannot.

Overall, these changes aim to improve clarity and consistency in merged results pipeline-related terminology. The changes affect JavaScript constants, Ruby code, localization, and documentation files.

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References

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• Refer to correct setting name for MR pipeline v... (!177082 - merged)