Refactor SSL_CTX_use_CryptoAPI_certificate()

Refactor SSL_CTX_use_CryptoAPI_certificate()

- Loading the certificate and key into the provider is split out of
  setting up the SSL context. This allows testing of signing by
  cryptoapi-provider interface without dependence on SSL context
  or link-time wrapping.

Change-Id: I269b94589636425e1ba9bf953047d238fa830376
Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230315013516.1256700-4-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26414.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>