[keyserver] Add node-fetch package

Summary:
Adds node-fetch package for making requests to the WNS. It's a 2.x.x version and not 3.x.x because the newest version fails on jest tests because it's ESM-only. A lot of people are facing this issue: SO post, discussion on gh. I've tried a few workarounds but I couldn't get it to work.

• 2.x.x is still getting security updated and bug fixes (the version I added here is from january 2023)
• there are no flow-typed types for 3.x.x versions
• fixing this issue might be connected to ENG-3414
• we are planning to move to fetch anyway after updating the node version D7253

Test Plan: yarn cleaninstall, check if CI passes

Reviewers: ashoat, tomek

Reviewed By: ashoat

Subscribers: atul

Differential Revision: https://phab.comm.dev/D7282