Make sure that the user won't unknowingly overwrite some internal data fields.

[ghost]

When a user logs something with additional data, using an internal data field has the bad behavior to overwrite a reserved internal key.
for instance:

reqLogger.info('text message', { name: 'pouet' });

here, the reserved internal field "name" will be overwritten.

We need to make sure this cannot happen in a default setting.

Such a behavior must be thought about for the default fields too.