Improve possibilities for monitoring storage operation as user.

[hg-ms]

Currently is very cumbersome to monitor storage actions like storing/deleting object from user API if logging is not sufficient. Maybe some extended functionality for monitoring may be useful for debugging.
This issue collects ideas how to improve Microstream monitoring:

1. Improve logging

• Add loggers that explicitly log storing or deletion of objects without other logs.
• Document / improve existing logging that could be helpful.

2. Add hooks that allow the user to add custom code in case of object storage or deletion.
   That way the user may collect all deleted Object Ids inside his app and run custom code here.

[hg-ms]

• Housekeeping statistics