Use rustls-tls-webpki-roots on Android

Summary: Current TLS backend for Rust websocket code on Android doesn't work since if cannot verify backup service certificate. We used to have similar issues with gRPC and we resolved them by updating tls backend to use webpki roots. This diff does the same on Android.

Test Plan:

1. Build physical Android app.
2. Toggle automatic backup upload and upload compaction to STAGING by clicking the upload button.
3. Ensure upload succeeds and new compaction is visible in dynamodb.
4. Type some drafts.
5. Ensure new logs are visible in dynamodb.
6. Log out and log in.
7. Click restore button.
8. Ensure restoration succeeds and drafts are brought back.

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11920