feat(agent)!: support both subnet id and canister id for certificate verification

[ilbertt]

Description

Supports both subnet id and canister id for certificate verification. The CreateCertificateOptions.canisterId field has been replaced with the principal field, of type:

type CertificatePrincipal =
  | {
      canisterId: Principal;
    }
  | {
      subnetId: Principal;
    };

How Has This Been Tested?

Same tests should still pass.

Checklist:

• My changes follow the guidelines in CONTRIBUTING.md.
• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.

[github-actions]

size-limit report 📦

Path	Size
@icp-sdk/core	91 B (0%)
@icp-sdk/core/agent	50.68 KB (+0.1% 🔺)
@icp-sdk/core/candid	13.31 KB (0%)
@icp-sdk/core/identity	20.55 KB (0%)
@icp-sdk/core/identity/secp256k1	33.75 KB (0%)
@icp-sdk/core/principal	4.44 KB (0%)