Require invite limit

[ekzyis]

Description

The frontend says invite limit is optional but if you don't enter anything and submit, we throw

Variable "$limit" got invalid value ""; Int cannot represent non-integer value: ""

I believe this has been an issue even before #1649 since the validation schema was not changed in #1649 and I had to update it to use .nullable().

Additionally, our code checked if invite.limit was defined everywhere except in the most critical part where it gets redeemed, lol.

Checklist

Are your changes backwards compatible? Please answer below:

yes

On a scale of 1-10 how well and how have you QA'd this change and any features it might affect? Please answer below:

6. Testing creating and redeeming limited and unlimited invite links.

For frontend changes: Tested on mobile, light and dark mode? Please answer below:

n/a

Did you introduce any new environment variables? If so, call them out explicitly here:

no

[huumn]

Given the way these are abused, I think the move is to make the limit required.

Since we merged user specified invite codes, having a limit is even more important, because we'll no doubt have people creating invite links like /invites/grayruby, ie the equivalent of people setting a password to password.

[ekzyis]

I see, makes sense, made the invite limit required for the mutation in f27be13 but didn't enforce it in the database because I am not sure how to deal with existing unlimited invites:

> SELECT COUNT(1) FROM "Invite" WHERE "limit" IS NULL;
256
> SELECT COUNT(1) FROM "Invite" WHERE "limit" IS NULL AND "revoked" = 'f';
179

I think we should first just make creating new unlimited invites impossible (this PR), announce that we will delete any unlimited invite in X weeks, then delete them and then make the Invite.limit column non-nullable.