[lib] Create hook for common RelationshipPrompt logic for web and native

Summary:
Created hook with logic from RelationshipPrompt native component, so it could be used also in web.
The hook has optional pendingPersonalThreadUserInfo param, as the web currently cannot create personal pending thread.

Test Plan: Tested the introduced hook with native and web (after changes in next diffs). The logic and behavior hasn't been changed and it works as before.

Reviewers: palys-swm, benschac, atul, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: benschac, ashoat, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D2845