Make OpenID4VCI implementation ready for general use

[reinkrul]

Nuts node can currently act as credential holder, requesting and receiving credentials from OpenID4VCI-compliant issuers. However, the feature is still in PoC/experimental state and needs to be explicitly enabled to be used. We bring it to a state in which it can reliably be used by e.g. Generic Functions data exchanges.

• Align with specification
  • Update OpenID4VCI implementation to spec v1.0 #3953
  • Align OpenID4VCI client with implementers draft #3152
• Update documentation