Improve master broken incidents by adding a 'Root cause analysis' thread

What does this MR do and why?

This implements the proposal from gitlab-org/quality/engineering-productivity/team#113 (comment 1184144461).

Example: gitlab-org/quality/engineering-productivity/master-broken-incidents-playground#22 (closed)

Screenshots or screen recordings

Title includes failing jobs (truncated to be less than the maximum of 255 characters)

Two threads are opened after the incident is created

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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