The bundle documentation uses `publicKeyIdentifier` instead of `publicKey` as element name

[mlschroe]

The example in the Public Key Identifier section in content/en/about/bundle.md seems to be wrong.

The protobuf specification contains

dev.sigstore.common.v1.PublicKeyIdentifier public_key = 1 [(google.api.field_behavior) = REQUIRED];

which gets translated into a json publicKey element name.