Provide hint when multiple config files are in-use

Sometimes an admin makes a copy of their config/config.php in their config/ folder without being aware of Multiple config.php file support. If named appropriately we load it up and merge it (as designed).

This scenario comes up in the support forum and our Issues, leading to avoidable support requests and invalid bug reports.

Since this typically comes up when the other config files are backups, the main symptom is: "Why aren't my config changes active?"

Maybe we can indicate somehow/somewhere when multiple config files are in-use. The trick is it is a perfectly valid mode of operation. We don't want it to be an error or warning in our setup checks. It's possible to have it be an info I guess? We also don't want it so subtle that it's not visible to someone that (a) isn't aware of multiple config file support (b) is trying to figure out why their config changes are getting "overridden".

Alternatives and related:

• Encouraging the use of occ config:list system (to see live merged config) rather than direct config.php access
• Show active (merged) config in the UI (i.e. equivalent to occ config:list system).

Start by tracing how multiple config.php files are loaded and merged, then compare the available context with the occ config:list system entry point. Done means users can clearly see that multiple configuration files are active, without treating the valid setup as an error or warning.