Update main.yml with cassandra (#3845)

ansible/roles/cassandra/defaults/main.yml

@@ -1,5 +1,5 @@
 user_home: "/home/{{ ansible_ssh_user }}/"
-cassandra_repo: 'deb http://www.apache.org/dist/cassandra/debian 311x main'
-cassandra_repo_key: 'https://www.apache.org/dist/cassandra/KEYS'
+cassandra_repo: 'deb https://debian.cassandra.apache.org 311x main'
+cassandra_repo_key: 'https://downloads.apache.org/cassandra/KEYS'
 resource_crunch: "yes" # make this value yes if heap size should be quarter of the Server Memory when you are deploying multiple databases, else make this value no to have 50% of the value as per the best practice of cassandra
 cassandra_home_directory: "/var/lib/cassandra"