Added a sample dag alert .

Infrastructure Submissions:

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• [YES] Have you added an explanation of what your changes do and why you'd like us to include them?
• [NO] I have updated the documentation accordingly.
• [NA] I have added tests to cover my changes.
• [YES] All new and existing tests passed.
• [YES] I have formatted the terraform code. (terraform fmt -recursive && go fmt ./...)

Current Behavior or Linked Issues

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Added a sample dag alert which triggers when the dag run duration of particular dag exceeds the threshold

Does this introduce a breaking change?

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• [YES]

Other information

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The output of the alert will be similar to the below.