Add new hook type: Trigger a plan

[oneisall8955]

I want a backup plan to be triggered when the plan completes. So I'd like to add a plan-type hook to the backrest that can be configured to fire when the plan is completed.

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Append: As you can see in the picture, I am editing the qiniu_software plan (a plan backing up my software configuration to a oss similar to S3).In the Hooks section, I want to add a Hook that triggers another task like bitiful_software (the trigger timing is On Finish Snapshot)