feat(crypto): CRP-2618 require omitting pre_signature_to_create_in_advance for vetKD

[fspreiss]

Adapts the registry canister and ic-admin so that for {Create|Update|Recover}SubnetPayload the KeyConfig's pre_signatures_to_create_in_advance field is no longer needed/allowed for vetKD keys (and generally for keys that don't have pre-signatures). So far, this field was always required, and for vetKD keys this was confusing because vetKD doesn't have the concept of pre-signatures.

The protobuf representation in the registry is unchanged, because there the pre_signatures_to_create_in_advance field was already optional. For existing registry entries for vetKD keys, the currently set value of 0 remains unchanged, while new entries that are created in the future will not have the field set any more.

This change is possible now that the registry canister was recently adapted (see Proposal 139679) to allow omitting pre_signatures_to_create_in_advance for keys that don't require it (#7859).

An alternative to this approach here would be to turn the ChainKeyConfig's KeyConfig into a protobuf enum. However, this would require an involved multi-step migration of registry data structures.

[mbjorkqvist]

Rubber-stamping DeFi change!

1. Done (updated unreleased_changelog.md).
2. No breaking changes, given that the KeyConfig::pre_signatures_to_create_in_advance field in the registry canister API was already optional.
3. No data migration needed.
4. No security review needed as not security critical.

[daniel-wong-dfinity-org]

Still approved.