[openssl/openssl] b544c7: Add ED25519 Signature demo.

[Shane]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: b544c72f3755c0ea51408d3118821a1ac126c070
      https://github.com/openssl/openssl/commit/b544c72f3755c0ea51408d3118821a1ac126c070
  Author: slontis <shane.lontis at oracle.com>
  Date:   2023-09-01 (Fri, 01 Sep 2023)

  Changed paths:
    M demos/README.txt
    A demos/signature/EVP_ED_Signature_demo.c
    M demos/signature/Makefile

  Log Message:
  -----------
  Add ED25519 Signature demo.

Reviewed-by: Tomas Mraz <tomas at openssl.org>
Reviewed-by: Matt Caswell <matt at openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove at arm.com>
Reviewed-by: Hugo Landau <hlandau at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21883)