[reports] Upgrade Postmark crate to fix TLS

Summary:
Resolves ENG-9819.

• Updated the postmark crate to the latest version which supports reqwest-rustls-tls feature. Added the feature.
• Addressed breaking changes - two API renames.

Test Plan:
Ran the service locally with e-mail config present. Sent a report.

• Before: Error from ENG-9819 appeared.
• After: E-mail was successfully delivered.

Reviewers: kamil, varun, will

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13973