[Nix] Add terraform to development shell

Summary:
For usage with AWS resources

https://linear.app/comm/issue/ENG-1997

Test Plan:

nix develop
which terraform # points to nix store

Reviewers: atul, varun, abosh, ashoat, O1 Nix

Reviewed By: atul, O1 Nix

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D5336