Allow admins to configure to redirect user to pub page after creating pub through public form

[tefkah]

Motivation

Currently when you create a pub through a public form you cannot see it again, and it's almost impossible for a user to find their pub unless they are very familiar with pubpub.

Requirements

• Allow admin to configure where to direct user after signup, one of these would ideally we the pub page.

Acceptance Criteria

Easy way would be to add PubValue token (ideally the pub id, not sure if that's possible yet) interpolation to the post submit page for public forms.

ive implemented the above in #1114