Add foreign key for ci_pipeline_chat_data.pipeline_id_convert_to_bigint

What does this MR do and why?

Add foreign key for ci_pipeline_chat_data.pipeline_id_convert_to_bigint

This is required so that we get all the indexes and foreign keys ready and can swap the columns of pipeline_id and pipeline_id_convert_to_bigint to complete the bigint conversion for pipeline_id

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Related to #422822 (closed)