[cli] switch to .tf.json over .tf for main/cluster files
[cli] switch to .tf.json over .tf for main/cluster files

* When using Hashicorp Config Language as JSON, it's best practice to store these files as .tf.json.
* This change removes old .tf files, which is necessary or else Terraform will read both .tf and .tf.json files in

airbnb/streamalert,airbnb/streamalert