Support retries

[firefart]

Is your feature request related to a problem? Please describe.
As most notification services are HTTP based and there can be network issues, it would be nice to have a retry option to retry each service x times an error. A global retry would be bad as it can result in double messages if only one service failed, so it should be per service.

Describe the solution you'd like
A retry count with an configurable additional sleep in between retries. The retry should be per service

Describe alternatives you've considered

Additional context