[Nix] Add awscli2 to dev shell

Summary:
Some services workflows may require
aws to create some cloud resources.

Part of https://linear.app/comm/issue/ENG-2649

Test Plan:

nix develop
which aws # should come to Nix store

Testing this thoroughly would include a workflow
which involves being setup with aws.

Reviewers: max, bartek, O1 Nix, varun

Reviewed By: bartek, O1 Nix, varun

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6285