Space creation: Unlimited email invites

### Your use case

From @niquewoodhouse :

How about something like this (quick prototype to explain idea)

**Main features**

- [ ] Adding content into the second email field creates an additional field beneath, so the list of emails just grows and grows¹
- [ ] When you have emails inputted and try to invite by username you get a warning sheet.

https://user-images.githubusercontent.com/1587166/149987090-8da1e979-42a1-4166-85fe-19ab58bcdc8c.mp4

**Notes**
¹ Maybe this one isn't as important as you can invite more people later.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

Start by locating the Space creation invitation flow in the iOS app and review the linked prototype video. Done means the email invite UI can add additional fields as emails are entered, and attempting a username invite while emails are present shows a warning sheet.

Written by the indexing model from the issue text.