Add audit log event for external module installs

[knolleary]

We currently log when nodes and installed and removed. This allows external systems to monitor what is being used.

We do not have equivalent audit events for dynamically installed modules used by the function node - we should fix that.

What is slightly complicated is we don't have quite the same lifecycle - there's no explicit uninstall action we can log to tidy things up. But better to be logging something rather than nothing.