[web] Add @matrix-org/olm dependency

Summary:
We need the Olm dependency in order to get device public key to include in SIWE message. (We may end up using the dependency for more things later on, but this is the only use case atm)

Including this dependency in browser isn't documented well, so I tried to get it to work based off of what I saw in other repos (eg jitsi-meet, element-web)

Test Plan:
Was able to import the dependency in web/account/siwe.react.js and run window.Olm.init() without issue.

Tested with dev and prod to ensure that we're able to init() Olm as expected.

Reviewers: ashoat, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D6400