OID4VC: support for richer issuer metadata as per later drafts of OID4VCI

[timbl-ont]

The current OID4VCI ACA-Py API does not support the creation and management of issuer metadata. In draft 11 of the OID4VCI spec this data was minimal and did not require any internal configuration. With later drafts, the issuer metadata has become richer in terms of optional parameters. The required parameters have not changed.

Of particular short term interest are the display properties which can be used in a wallet without any other code changes to the plugin. Other properties will be important as features are added in support of later drafts of the specification - e.g batch endpoint, nonce endpoint etc...

This issue is to track the creation of CRUD API endpoints to manage the issuer metadata. The credentials supported metadata should be appended to the issuer metadata (many to one) as per https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html (section 11.2.3)

The required parameter credential_endpoint should be configured at startup and the credential_issuer endpoint should be generated if not defined via the API (as per current design)