export: Add missing datetime fields for post-processing.
export: Add missing datetime fields for post-processing.

datetime objects are not ordinarily JSON serializable.  While both
ujson and orjson have special cases to serialize datetime objects,
they do it in different ways.  So we want to fix the post-processing
code to do its job.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,zulip/zulip,brainwane/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,kou/zulip,showell/zulip,showell/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,kou/zulip,showell/zulip,punchagan/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,zulip/zulip,showell/zulip,brainwane/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,andersk/zulip,brainwane/zulip,eeshangarg/zulip,punchagan/zulip,brainwane/zulip,kou/zulip,rht/zulip,showell/zulip,andersk/zulip,kou/zulip,showell/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,punchagan/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,showell/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,hackerkid/zulip,brainwane/zulip,brainwane/zulip,kou/zulip