DATE not parsing rfc3339 correctly

[fundef1]

Describe the bug
DATE not parsing rfc3339 string correctly
2

To Reproduce
in https://www.montferret.dev/try/

LET dateString = "2021-08-29"
LET dateTime = DATE(dateString)
return dateTime

Expected behavior
a dateTime object, rfc3339 allows YYYY-MM-DD as a valid datetime string
at least according to ​https://ijmacd.github.io/rfc3339-iso8601/
although I guess you could argue that it's a full-date and not a date-time.

anyway some easier way of converting date(time) strings into datetime would come in handy

Screenshots

"error": "run program: parsing time \"2021-08-29\" as \"2006-01-02T15:04:05Z07:00\": cannot parse \"\" as \"T\": DATE(dateString) at 5:15"

Additional context
manually adding the remainder of an rfc3339 datetime works around the issue,

LET dateString = "2021-08-29"
LET dateStringFixed = CONCAT(dateString,"T00:00:00.00Z")
LET dateTime = DATE(dateStringFixed)
   ​T::DATETIME(dateTime)
return dateTime
``

[ziflex]

Well, this part is handled by Go's standard library.
I guess the most suitable fix would be to allow passing an alternative string layout to the function.