[web-db] add database module provider

Summary:
Making database connection accessible from entire web app

Depends on D7188

Test Plan:
Check how it behaves in multiple places in web app, try sending some worker messages, e.g.:

databaseModule
  .schedule({
    type: workerRequestMessageTypes.GET_CLIENT_STORE,
  })
  .then(e => {
    console.log(e.store.drafts);
  })
  .catch(e => {
    console.error(e);
  });

Reviewers: michal, tomek

Reviewed By: tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7189