feat: add Extension trait for SIOPv2 and OID4VP

[nanderstabel]

Description of change

This PR includes several changes:

• Use of JsonValue instead of serde_json::Value
• Refactor of AuthorizationRequest (in oid4vc-core/src/authorization_request.rs) which means the previous awkward RequestUrl is deprecated. Possible variations of AuthorizationRequest are now: AuthorizationRequest<ByValue>, AuthorizationRequest<Object>, AuthorizationRequest<Object<SIOPv2>>, and AuthorizationRequest<Object<OID4VP>>.
• A new Extension trait (defined in oid4vc-core/src/openid4vc_extension.rs), which allows for a clearer distinction between oid4vc-core, siopv2 and oid4vp. The core part of both AuthorizationRequest and AuthorizationResponse or now moved to the oid4vc-core crate.
• ClientMetadata and Scope are moved to oid4vc-core as well now.
• Upgraded ed25519_dalek dev-dependency.
• Temporary removed the outdated iota DID method.

Links to any relevant issues

#42

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