Pull Request which spans multiple pipelines sometimes fail to start all jobs

[jithine]

What happened:
We notices an instance where a Pull Request which was supposed to start 18 jobs was not starting all of them.

{ "level": "error", "message": "[e2eab260-7971-11ec-9b73-901c677be0cd]: SequelizeUniqueConstraintError: Validation error", "timestamp": "2022-01-19T21:51:09.693Z" }
20119/215059.000, (1642629059000:sdapi-7f48cc6446-thlcw:27:kyeapnkn:63693) [response,api,webhook] 

What you expected to happen:

Erroneous pipelines should not block rest of jobs from starting up. In this instance there was an error in one of the pipelines (probably) which prevents all events from being processed properly.
Expectation would be SD API should run all jobs which can run and log the ones which it's unable to run.

How to reproduce it:

N/A

[jithine]

https://github.com/screwdriver-cd/screwdriver/pull/2641/files

[jithine]

this issue is caused by a DB unique key constraint which is not quite valid for a single git repo with multiple pipelines created with source dir.

https://github.com/screwdriver-cd/data-schema/blame/master/models/event.js#L169

All such events will same same sha and potentially same createTime We need to either undo the DB constraint or make event creation sequential.