Write ADR for X509 Verification of Matrix devices

Problem:

• To increase trust against other users and avoid expose of personal data it is required that only authorized devices can connect to BundID services.

Goal:

Define how X509 device verification will work for public agencies.

ACs:

• Outline X509 device verification process.
• Discuss security considerations (Do we have to discuss server side or X509 certificate issuing threats?)
• Requirements for multi device (verification for each device versus verification on signing key base).
• Create ADR.
• Document ADR here -> https://gitlab.opencode.de/fitko/matrix-g2x/solution-architecture/-/blob/main/09_architecture_decisions.md

Notes/ resources:

• Related ticket: #2
• Requirements uIDs: Zapuk_109; LB_32; LB_36; LB_38