Bug 30310: Fix date_to_rfc3339

Bug 30310: Fix date_to_rfc3339

We need the customParseFormat plugin to provide a custom date format to
the dayjs constructor.
Found while working on bug 32559, don't remove this function, it will be
used later.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit dded614fa1735f35b0ee34869f5e45b87262382b)
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>