org settings: Change user joining invitation setting to dropdown.

[shubhamdhama]

Last followup of #9071 (comment)
GIF:

[shubhamdhama]

Feedback regarding strings required!
@timabbott @rishig FYI.

[rishig]

Great, thanks!

• Let's flip the order of the two settings, so the email domain one comes second
• Let's call the email domain one "Email domains of new users" rather than "Restrict email domains of new users".

For the text of the new settings, maybe:

Invitations
* No invitation required to join
* Anyone can invite new users 
* Only admins can invite new users

[timabbott]

I'm not sure I like how the last two read, in the context of reading what the current state is without clicking into the dropdown. Maybe:

Invitations for creating accounts:

• Not required.
• Required; any user can send invitations.
• Required; only organization administrators can send invitations.

[rishig]

Seems reasonable. This is right below "Joining the organization", but we could also do
Invitations for joining the organization
as the label?

Styling notes for when this is implemented

• No periods at the end (and no : at the end of the label)
• "organization administrators" is "admins" in settings dropdowns.

[shubhamdhama]

@rishig @timabbott Does this looks good?

[rishig]

Thanks @shubhamdhama! One more attempt; I think this is better than the ones so far :).

Are invitations required for joining the organization?
* No
* Yes, and anyone can send invitations
* Yes, and only admins can send invitations

[shubhamdhama]

@rishig Here are various screenshots of the dropdown, let me know how this looks ow?

[rishig]

lgtm, thanks! To make the second setting parallel to the first, we could go back to Restrict email domains of new users?, but with a question mark at the end.

[timabbott]

I think we want this to set invite_by_admins_only = false as well, right? Just from a general cleanlyness perspective.

[shubhamdhama]

@rishig @timabbott updated(waiting for tests to get passed)

[timabbott]

@shubhamdhama looks great, though I'd put that text change for the second dropdown into its own commit.

[shubhamdhama]

Ahh sorry, I'll keep this in mind!
(updated)

[timabbott]

Merged, after changing the "anyone" to "normal users"; I think it's important to distinguish users from "people on the internet", and also, we'll eventually want to talk about "normal users" to distinguish from guest users.