Add intial nix yarn dev env

Summary: Add initial nix dev environment for yarn workflows

Test Plan:

• Install nix and flakes (out of scope for this PR, part of D2921)
• Run nix develop
• Do workflows which require yarn

Reviewers: atul, palys-swm, karol-bisztyga, geekbrother, jimpo, varun, ashoat

Reviewed By: palys-swm, jimpo, varun, ashoat

Subscribers: varun, ashoat, palys-swm, Adrian, atul, karol-bisztyga, benschac

Differential Revision: https://phabricator.ashoat.com/D3274