[Nix] Add bundler for pod install

Summary:
Allow for bundler to be used for pod install

https://linear.app/comm/issue/ENG-2198

Test Plan:

nix develop

which bundle # shound point to nix store

cd native
bundle install

cd ios
bundle exec pod install

Reviewers: atul, varun, ashoat, O1 Nix

Reviewed By: atul, ashoat, O1 Nix

Subscribers: tomek, abosh

Differential Revision: https://phab.comm.dev/D5565