[lib] move olm utils from keyserver to lib

Summary: we can reuse these on web, too, so moving them out of keyserver

Test Plan: able to log in to staging identity service from my local keyserver after clearing the metadata table

Reviewers: ashoat, kamil, marcin

Reviewed By: ashoat, marcin

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D10876