feat: new util class expected for return errors by more convenient way

Source: https://github.com/TartanLlama/expected

Also it adds util/expected.h to exclude list of our linters

Author: knst

src/Makefile.am

@@ -324,6 +324,7 @@ BITCOIN_CORE_H = \
   util/enumerate.h \
   util/epochguard.h \
   util/error.h \
+  util/expected.h \
   util/fastrange.h \
   util/fees.h \
   util/golombrice.h \