botan3: init at 3.1.1
Use the existing generic botan file and add specialization
for botan 3. Botan 3 most importantly adds support for
TLS 1.3 and PQC algorithms. Introduce Botan 3 in parallel to
Botan 2, as it is a major release and e.g. now uses C++20
in contrast to C++11 of Botan 2.9.
Signed-off-by: Markus Theil <theil.markus@gmail.com>