Run evaluation in merge request pipelines when Duo feature is changed

Problem

We currently manually run evaluations in Prompt Library or ELI5 projects. This is not practical because:

• Developers have to setup and run an evaluation pipeline in their local environment everytime they change a Duo feature.
• Developers can merge a change without running evaluations.

Target changes

• Model
• Prompt
• Input Parser
• Output Parser

Proposal

• Run the evaluation pipeline in merge request pipelines when Duo feature is changed. This includes both GitLab-Rails and AI Gateway.
• Fail the job when it detects a quality degredation, which effectively prevents developers from merging it.
• Introduce a new label to skip the job in emergency. (like pipeline:skip-undercoverage)