Fixes #5320: update technique to understand the error only mode

I would rather define this as a default for now - something like:

```
"full_compliance" expression => "!changes_only";
```

(obviously after the definition of ```changes_only```)

The point being to fallback to this mode, even if the ```RUDDER_REPORT_MODE``` variable is not set or not set correctly. The last thing we want is to break reporting.