[7/n] [landing] lift request access function up to landing page

Summary: this function needs to be used in the header and app-landing component. Lifting it up so I can pass it down later

Test Plan: Make sure the request access button works in the header

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga, boristopalov

Differential Revision: https://phabricator.ashoat.com/D2557