Backend: Implement strategy: mirror

Problem

Users would like to mirror a more accurate status of a downstream pipeline in a trigger job to alleviate some of the confusion however there is some inconsistency with some of the scenarios when using strategy: depend

Proposal

introduce a new keyword strategy: mirror which will mirror DSP status in a trigger job

statuses should mirror as below:

trigger job status	downstream pipeline status
skipped	manual skipped
blocked	manual blocked
if allow_failure: true passed with warnings failed	failed passed with warnings
failed with warnings	failed with warnings

NOTES:

• Trigger job status "skipped" when the DSP is "manual skipped"
• Trigger job status "blocked" when the DSP is "manual blocked"
• When Trigger job is allow_failure: true trigger job status is "passed with warning" when the DSP is "failed"
• Trigger job status "failed with warnings" when the DSP is "failed with warnings"