libwebsockets: full variant provides OpenSSL

libwebsockets: full variant provides OpenSSL

For some time, it is not possible to install ttyd and mosquitto-ssl at the
same time, so let's solve it that libwebsockets-full provides
libwebsockets-openssl. This allows to install ttyd and mosquitto at
the same time.

Also, we need to add conflict, because we should not have installed
libwebsockets-openssl and libwebsockets-full at the same time as they
provides the same files.

Signed-off-by: Josef Schlehofer <redacted>