MEDIUM: ssl: support for ECDA+RSA certificate selection with AWS-LC

MEDIUM: ssl: support for ECDA+RSA certificate selection with AWS-LC

AWS-LC does not support the SSL_CTX_set_client_hello_cb() function from
OpenSSL which allows to analyze ciphers and signatures algorithm of the
ClientHello. However it supports the SSL_CTX_set_select_certificate_cb()
which allows the same thing but was the implementation from the
boringSSL side.

This patch uses the SSL_CTX_set_select_certificate_cb() as well as the
SSL_early_callback_ctx_extension_get() function to get the signature
algorithms.

This was successfully tested with openssl s_client as well as
testssl.sh.

This should allow to enable more reg-tests that depend on certificate
selection.

Require at least AWS-LC 1.22.0.