Add generic secret skeymgmt provider, skey abstraction and default skeymgmt

Add generic secret skeymgmt provider, skey abstraction and default skeymgmt

This commits adds an actual skey wrapper structure and skeymgmt
implementation for the default provider

This allows to use fallbacks for any SKEY operation,
and to use it for keys that do not have a specific purpose and
cipher-suite associated to it.

Add a test with a key type that does not have skey support (DES),
to show that the fallback works.

Add raw skey test

Signed-off-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/26753)