Add an option to print which reachability metadata files are picked up

[loicottet]

Feature request

Is your feature request related to a problem? Please describe.
When a specific configuration entry is not picked up by the Native Image builder, it is sometimes confusing to understand whether this is caused by a mistake in the configuration or by the file not being picked up by Native Image

Describe the solution you'd like.
A flag that can be used to print all configuration files parsed by the program.

Describe who do you think will benefit the most.
GraalVM users who face issues with reachability metadata.

Express whether you'd like to help contributing this feature
I will implement this feature.