tutorials shouldn't be susceptible to topic retention deleting sample data

The root cause of [this](https://github.com/confluentinc/kafka-tutorials/issues/1333) issue is that the sample row timestamps are beyond the default topic retention period, so recipe flow breaks, e.g., final table output in that recipe sometimes won't show up because source data is gone.

This deserves a sweep of the repo (e.g., search for years -- [2020](https://github.com/confluentinc/kafka-tutorials/search?q=2020&type=code), [2021](https://github.com/confluentinc/kafka-tutorials/search?q=2021&type=code)), and either fix (change retention, ksqlDB recipes could use `FROM_UNIXTIME(UNIX_TIMESTAMP())`) or open follow-on issues for complex cases. Automated tests may need to be reworked to support dynamic times.