fix: Fix job start

[minghay]

Context

When starting a new event from a job in the V2 job UI, the event is started from ~commit instead of the selected job.

Objective

1. Update the title on the start event button to better capture that an event will be started from the event
2. Update the start modal to provide the job information
3. Update the post body to handle a couple new scenarios

References

screwdriver-cd/screwdriver#3200

License

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