If public key passed as header (`siwePrimaryIdentityPublicKey`), we'll incude it in the SIWE message statement.
For the timebeing if a `siwePrimaryIdentityPublicKey` is NOT being passed in as header, we'll fallback to the previous SIWE message statement without the public key. Will go back and enforce existence of `siwePrimaryIdentityPublicKey` (with necessary error handling, error messages, etc) later in the stack.
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Depends on D6131