[web] Hide databaseModule behind a function

Summary:
Part of ENG-4844
When database will be used by all users (including anonymous ones), we need to make sure that it's never in an unitialized state. We hide it behind a getter function so we add the initialization code there in the later diffs.

Test Plan: yarn flow

Reviewers: kamil, tomek, inka, atul

Reviewed By: kamil, tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9105