[Dashboard] Fix dashboard for daylight savings

Did not get traction with the holistic fix for daylight savings
as there was pushback on usage of tzlocal in python. So,
splitting out the fix on the UI side which is perhaps less
controversial.

On the UI side, `timezone.ts` is showing GMT offsets not reflective
of daylight savings time. Updating to dynamically pull the offset
from `Intl.DateTimeFormat`. Note not doing any dynamic evaluation
so for browser windows open during the switch, it will not update.

Signed-off-by: Brendan Miller <6900229+bhmiller@users.noreply.github.com>

Author: bhmiller