IssueCollector class
A collection of configuration issues (instances of class Issue).
IssueCollector is a generic class that collects issues detected during the validation
process. In particular, an IssueCollector is created and returned by the Config.check()
method. It contains all the collected issues separated by severity (ERROR, WARNING, INFO).
Each issue is an instance of the class Issue and contains the necessary information to
understand the issue and help the user to fix it.