[S2S] Atomic Credential Sets

This feature is to be able to support some form of:

Multiple Credential Datasets issued to a particular Wallet Client Instance from the same verification session that need to be updated together, share Credential Metadata (or only one has the metadata) and can't be in different states.

This is something of the form of:

• When a management operation occurs it either succeeds for all of them or none of them
• When a version update happens, it occurs for all credential instances at the same time, so there is no version skew between them
• Credential Metadata is only returned for the 'primary' one and the Wallet Client is aware that these are related.
• (Potentially): each individual cryptographic object is 'linked' between the credential instances (e.g. if you want to do per-presentation linking in a privacy preserving way)

@martijnharing to clarify some of the illustrative examples/requirements here.

Some examples that (may) fall under this category:

• Multi-format Issuance (Same Dataset in different Credential Format)
• Age_over_xx values changing from the same Dataset, pre-issued at the same time
• Linked Datasets that need to be updated in sync (Passport + Visas)

Today, this can only be solved with a Wallet fan-out and OOB knowledge of how to merge/fail etc.

Solution space includes:

• Wallet Server fan-out, with linked information provided by issuer as a CredentialSet
• Have 'sub-credential' identifiers under CredentialInstanceIdentifier, allowing more complex Credential Configuration
• Package this within the Credentials returned (as a CredentialBundle)

Note: this feature applies to canonical VCI as well

Start by turning the stated atomicity, shared metadata, synchronized versioning, and optional cryptographic-linking requirements into a precise model for canonical VCI. Compare the listed wallet fan-out, sub-credential identifiers, and CredentialBundle approaches; done means one agreed solution with clarified examples and requirements.