Start working on mask command

src/database/migrations/0004_participant_is_masked.cql

@@ -0,0 +1,6 @@
+ALTER TABLE payphone.participants ADD is_masked BOOLEAN;
+
+CREATE MATERIALIZED VIEW IF NOT EXISTS payphone.participants_by_user_id AS
+    SELECT user_id, call_id, channel_id FROM payphone.participants
+    WHERE user_id IS NOT NULL AND call_id IS NOT NULL AND channel_id IS NOT NULL
+    PRIMARY KEY (user_id, call_id);