GRAMEX-206 ⁃ Schedules should support an error alert

[sanand0]

When a schedule fails, users are unaware of it unless they look at logs.

Allow schedules to support an error-alert: config that specifies the error alert to call. For example:

schedule:
  run-periodically: mymodule.myfunction()
  every: 6h
  error-alert: email-admin

alert:
    to: '[email protected]'
    subject: 'Gramex raised an Exception'
    body: ...

If there's an exception, this sends an email using the alert.

┆Issue is synchronized with this Jira Bug

[sanand0]

Note. We might want to extend this to a general error alert schedule, that captures all error logs and emails them at a developer-decided frequency.