Added support for suffix on database and/or collection

[nanny07]

Summary

This PR introduces the ability to add dynamic suffixes to MongoDB database name and/or collection names in the NLog.Mongo target, enabling more flexible log organization and partitioning strategies (ex. multi tenants)

Changes Made

• Added databaseSuffixProperty and collectionSuffixProperty to MongoTarget to identify which bson property needs to be read to get the suffix.
• Updated the collection and database's resolution based on the properties above
• Updated tests to validate suffix functionality and to show how to configure the property

Fully backward compatible