[FEAT] Use the Notifications System in Backstage to notify when there is an issue with OPA

[Parsifal-M]

Is your feature request related to a problem? Please describe. Something that came to mind when looking into #218 is that if you fall back to say a deny/allow/fail you probably want to be notified that there could be an issue with OPA.

You could set a config value under here once we add policyFallback we could add another value maybe notifyGroup or/and notifyUser and have them receive notifications that there is an issue.

Describe the solution you'd like Using the notifications framework and based on advice by @drodil we could do something like:

1. You can do it pretty easily to OPA plugin directly, you just need probably a config value that contains notification receivers in case of error and add notificationService as optional dependency to the plugin. For this you also probably need a scheduled task to check the status periodically.

2. If it makes sense to use the existing devtools plugin, that would require first a scheduled task to check for the endpoints (+ i would add support for caching as it's possible to generate quite a lot of requests to external systems with this) and secondly support for notifications

Describe alternatives you've considered I think we can always go for Option 1 initially then also look at adding option 2 later on if we can.

Additional context N/A