All system properties and environment variables should be accessed via the new CassandraRelevantProperties and CassandraRelevantEnv classes

Follow up ticket for CASSANDRA-15876 - 
"Always access system properties and environment variables via the new CassandraRelevantProperties and CassandraRelevantEnv classes"
As part of that ticket we moved to the two new classes only properties/variables that were currently listed in System Properties Virtual Table.
We have to move to those classes the rest of the properties around the code and start using those classes to access all of them. 

Additional information for newcomers:

You might want to start by getting acquainted with CassandraRelevantProperties and CassandraRelevantEnv classes. Also, you might want to check what changes were done and how the first batch was transferred to this new framework as part of  CASSANDRA-15876

We are interested into the properties accessed currently through getProperties around the code.

As part of CASSANDRA-15876 relevant unit tests were added (CassandraRelevantPropertiesTest). To verify the new patch we need to ensure that all tests Cassandra pass and also to think about potential update of the mentioned test class.