[landing] introduce competitors type

Summary:
As I was working on addressing some feedback to competitor feedback cards, I wanted to reuse the values of competitors as a type in the competitor card component and competitor logo component. This diff creates the shared type

Depends on D7904

Test Plan: flow, everything still works

Reviewers: atul, kamil

Reviewed By: atul

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D8016