Allow Time Bucket Function to Accept Floats and Timestamps

Drill has a function `time_bucket()` which facilitates time series analysis. This PR extends this function to accept `FLOAT8` and `TIMESTAMPS` as input.  Floats are typically not used for timestamps, however in the event that the data is coming from imperfect files, the numbers may be read as floats and hence require casting in queries.  This PR makes this easier.