How to prevent broken master with merge trains & pipelines

What this post added

Introduced and explained 'Pipelines for Merged Results' which runs CI pipelines on merge commits generated from the latest target and source branches before merging, providing an 'untrusted' pipeline result. Also introduced 'Merge Trains' as a queueing system to avoid race conditions between concurrent merges by creating sequential merge commits and running pipelines on them, dropping problematic MRs from the train.