not being able to create members during group creation breaks workflows

[r10s]

there is a longer standing issue that you cannot ~~add~~ create members during group creation (as on android or ios).

the the past, this was only a comparable small inconvenience as you could create the group beforehand and create and add members later - so at lease you do not have to throw aways the group.

meanwhile, we create guaranteed-e2ee groups if possible by the initial member list - and that makes it impossible to add email addresses later.

eg. this is a typical workflow for using delta chat to send a comparable "normal looking" mail to somebody, eg. some company's info@company address you did not wrote to before:

1. create a group with group name == subject
2. create and add info@company
3. write a message, maybe attach a pdf or so

in the past, that works like that - meanwhile, you cannot add info@company in step 2. as in step 1. a guaranteed-e2ee groups is created.

theoretical fixes may be to not create guaranteed-e2ee in this case (as already discussed in the past) or to allow setting the subject differently, however, both would be some effort and/or may have other downsides.

pragmatic fix would be to allow adding members during group creation - which is very useful in general, independently of who subject can be set or how guaranteed-e2ee is determined.