alertmanager proposal: make retrier configurable via slack.New

[Péter Laukó]

Hi,

I would lik to propose making retrier configurable in slack.Notifier by adding it as a parameter to slack.New. This would allow providing a Retrier.CustomDetailsFunc externally.

We have a custom go admin application for alert rules and notifications that allows configuring alertmanager to our users and we have a feature of sending test notifications. We use alertamanger as a library. When the user provides an invalid slack url e.g. https://slack.com/whatever slack returns a huge 404 page that looks bad in our ui's error message. Right now we need some regexp magic to filter out these errors, and it would be much more elegant if we could provide our own CustomDetailsFunc implementation.

This idea is related only to the slack.New function when used as a library, it does not affect alertmanager configuration as a standalone application. Please let me know if it makes sense, and I'm happy to provide patch.

Best,

Peter