text: CREATE TABLE IF NOT EXISTS chat_conversations(
      id                  BIGSERIAL                   NOT NULL PRIMARY KEY,
      started_ts          TIMESTAMP WITH TIME ZONE    NOT NULL,
      end_ts              TIMESTAMP WITH TIME ZONE    NOT NULL,
      conversation_type   VARCHAR(32)                 NOT NULL,
      vanishable          BOOLEAN                     NOT NULL
  );
  
  CREATE TABLE IF NOT EXISTS chat_user_x_conversation(
      user_id             BIGINT REFERENCES chat_users(id),
      conversation_id     BIGINT REFERENCES chat_conversations(id),
                          PRIMARY KEY (user_id, conversation_id)
  );