SpringBoot Push SslBundleProperties.key property down to JksSslBundleProperties

Having a key property on PemSslBundleProperties makes no sense because it's impossible to add a PEM key with a specific alias or password. I think we can safely push it down to JksSslBundleProperties. Since it's not possible to use it in Spring Boot 3.1, we can hopefully skip the deprecation step.

Comment From: philwebb

Looking again in 3.1 we do pass the key alias property to the PemSslStoreBundle.

Comment From: philwebb

Superseded by #38125