ADR: Decide if we want to implement E2EE between ZBP bridge and app/web client

Problem:

• After a bridge between the ZBP BE and the Matrix home server is built the bi-directional post box migration can start.
• However, should the migration from the ZBP BE to the Matrix home server introduce e2ee?

Goal:

Clarify whether the ZBP <-> Matrix BE migration implements e2ee.

ACs:

• Describe the steps required to conduct the migration.
• Define whether the bridge should en/decrypt data towards/from matrix (end to bridge encryption, e2be).
• Document results in this ticket.

Notes/Resources:

See more about post box migration here, chapter 2