Add the diffblue-opensource team as codeowners for the new C++ api

Author: NlightNFotis

CODEOWNERS

@@ -38,7 +38,7 @@
 /jbmc/src/java_bytecode/ @romainbrenguier @peterschrammel
 /src/analyses/ @martin-cs @peterschrammel @chris-ryder
 /src/pointer-analysis/ @martin-cs @peterschrammel @chris-ryder
-
+/cpp_api/ @diffblue/diffblue-opensource
 
 # These files change frequently and changes are medium-risk