MTM-57112 Add caution about reduced storage limits to user documentation

[rohitjoshi-c8y]

This PR adds an important notice to the user documentation regarding upcoming changes to the storage limits for microservice-based data broker. I was told that customers rarely read the change logs, so perhaps this could help. Anyways, we have also contacted customers who are likely to be impacted by this change individually through CSMs, so they are covered.