[web-db] add Shared Worker config

Summary: Adding config and file for shared worker.

Test Plan:
Run this code:

const webDbWorker = new SharedWorker('/worker/webDatabase');
webDbWorker.port.onmessage = function (e) {
  console.log('message from worker: ', e.data);
};
webDbWorker.port.postMessage('hello there from main thread');

and check results in browser, desktop and shared worker consoles.

Reviewers: michal, tomek

Reviewed By: michal, tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6987