A CalendarPeriod represents the abstract concept of a time
period that has a canonical start. Grammatically, "the start of the
current CalendarPeriod". All calendar times begin at 12 AM US
and Canadian Pacific Time (UTC-8).
Values:
CALENDAR_PERIOD_UNSPECIFIED (0):
Calendar period is unset. This is the default
if the budget is for a custom time period
(CustomPeriod).
MONTH (1):
A month. Month starts on the first day of
each month, such as January 1, February 1, March
1, and so on.
QUARTER (2):
A quarter. Quarters start on dates January 1,
April 1, July 1, and October 1 of each year.
YEAR (3):
A year. Year starts on January 1.
