Clarify the implementation path for the Matrix Rust SDK

Problem:

• We need to integrate the Matrix Rust SDK with the web client and the iOS app.
• How will this be done?

Goal:

Clarify the technical steps for integrating the Matrix Rust SDK with the web client and iOS app.

ACs:

• Briefly onboard Element Rust SDK specialist.
• Define the path for integrating the SDK (clarify open points).
• Define tasks and next steps. (Define Spike tickets)
• Define ACs for implementing the Rust SDK.
• Add them to #169 and #170
• Document results in this ticket.

Note/ resources:

• See linked issues