upload: Add --draft-on-create-only

[jerry-skydio]

When set, the Draft: tag only applies when the pr is created, so a pr that
the user marks ready for review in github stays that way.

[jerry-skydio]

Reviews in this chain:
└#297 upload: Add --draft-on-create-only
　└#298 upload: Add --deep-stack-draft
　　└#299 upload: Pass pushed refs to the pre-upload command

[jerry-skydio]

#	head	base	diff	date	summary
0	af43a3c3	0e5c3632	diff	Sep 11 14:51 PM	5 files changed, 59 insertions(+), 3 deletions(-)
1	eb4c1134	8e33338d	rebase	Sep 11 14:58 PM	0 files changed
2	297d71c6	09ceb4dc	diff	Sep 15 13:20 PM	0 files changed

[aaron-skydio]

should we default this option on for revup users?

it seems like a good default, although how you want to think about backwards compatibility of options like this

[jerry-skydio]

i'll defer changing it for everybody atm, we can't predict what the most common workflow for all users is. i think there could be points made for either side of this flag