Change license to the Apache License v2.0

This applies to the 'master' git branch and OpenSSL version 3.0.0 and
up.  Pre-3.0.0 versions retain the previous license.

The boilerplate will change in increments after this change.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7764)