Add support for INTERVAL / TIMESPAN datatype in Pinot

The `INTERVAL` datatype will allow users to manipulate a period of time in years, months, days, hours, minutes, seconds, etc

Example of use:
```
SELECT
now(),
now() - INTERVAL '1 year 3 hours 20 minutes'
```

Postgres reference - https://www.postgresql.org/docs/current/datatype-datetime.html