SSL channel args work with client config again

src/core/channel/channel_args.c

src/core/channel/channel_args.h

src/core/security/client_auth_filter.c

src/core/security/credentials.c

src/core/security/server_secure_chttp2.c

src/core/surface/channel_create.c

src/core/surface/secure_channel_create.c

test/core/end2end/fixtures/chttp2_simple_ssl_fullstack.c

.../end2end/fixtures/chttp2_simple_ssl_fullstack_with_poll.c

...nd2end/fixtures/chttp2_simple_ssl_with_oauth2_fullstack.c