Improve Execution Notifications plugins to allow passing custom payload

[wrussell1999]

Feature description

Add the ability to be able to get the {{ errorLogs() }} function inside of a Flow Trigger that runs when flows fail. This allows for instance wide error handling with useful errors inside of them.

From a user in Slack:

I'm using a triggered Slack alert flow for all failed flows in my workspace as described in best practices here. Is there any way to get the new {{ errorLogs() }} pebble function from the v0.20 release into the trigger attributtes, so that my Slack alert flow can display them? (without having to push it into outputs for every single flow)