Add support for OpenSSL 3.0

[janlindstrom]

See https://jira.mariadb.org/browse/MDEV-25785

[temeo]

Installed OpenSSL 3.0.0:

$ ./Configure --prefix=/usr/local/OpenSSL_3.0.0 --libdir=lib
$ make && sudo make install

Built Galera with OpenSSL 3.0.0:

$ cmake -DOPENSSL_ROOT_DIR=/usr/local/OpenSSL_3.0.0
...
-- Found OpenSSL: /usr/local/OpenSSL_3.0.0/lib/libcrypto.so   
-- /usr/local/OpenSSL_3.0.0/lib/libssl.so;/usr/local/OpenSSL_3.0.0/lib/libcrypto.so
-- GALERA_SSL_LIBS: /usr/local/OpenSSL_3.0.0/lib/libssl.so;/usr/local/OpenSSL_3.0.0/lib/libcrypto.so
...
$ make && make test
...
100% tests passed, 0 tests failed out of 7
...
$ ldd ./libgalera_smm.so  | grep ssl
	libssl.so.3 => /usr/local/OpenSSL_3.0.0/lib/libssl.so.3 (0x00007fe5d1adc000)

Seems to work for me out of the box.

[temeo]

Closing as MDEV-25785 has been resolved.