Support INTERVAL data type

"BigQuery now supports the [INTERVAL](https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#interval_type) type, which represents a duration or an amount of time. This type is in Preview."

https://cloud.google.com/bigquery/docs/release-notes#July_27_2021

An INTERVAL object represents duration or amount of time. Interval is composed of three independent parts:

• [sign]Y-M: Years and Months
• [sign]D: Days
• [sign]H:M:S.F: Hours, Minutes, Seconds and Subseconds.

Canonical format

[sign]Y-M [sign]D [sign]H:M:S[.F]

• Y: Year
• M: Month
• D: Day
• H: Hour
• M: Minute
• S: Second
• [.F]: Up to six fractional digits (microsecond precision)

TODO:

- [ ] Add relevant enums for data types
- [ ] Row data is converted to relevant type in RowIterator (`list_rows()`) https://github.com/googleapis/python-bigquery/pull/840
- [ ] Convert data type in query parameters
- [ ] Covert data type in `insert_rows`

Edit: Removed pandas, arrow, db-api support in favor of https://github.com/googleapis/google-cloud-python/issues/15279, as those implementations are currently blocked on Arrow and the BQ Storage API.