Draft agenda for TPAC 2023.

Hey folks,

Based on the discussion in https://github.com/w3c/webappsec/issues/627,
I've put together a draft agenda for our meetings on Thursday and Friday:
https://github.com/w3c/webappsec/blob/main/meetings/2023/2023-09-TPAC-agenda.md.
Looking forward to seeing y'all there!

If you have feedback on the agenda, or requests for
additions/removals/reshuffles, please add them to the thread at
https://github.com/w3c/webappsec/issues/627.

Thanks!

-mike