conf: load conf node tree from new yaml loader

Use Rust to parse the Suricata configuration, then transform the parsed
YAML document into our Conf tree on the Rust side.

This keeps the Conf API as-is, but removes the dependency on libyaml for
loading the configuration.

The next step would be to remove the Conf node tree and just back it
with the Yaml data structure.

Breaking changes:

- no longer parsed as NULL: Null, nUll, etc. Just null and NULL are
  parsed as NULL, as this is more YAML compliant
- Multiple include keywords at the same level will no longer work. We
  deprecated this in 7.0, but continued to support it, see
  https://redmine.openinfosecfoundation.org/issues/5939

Author: jasonish

configure.ac

@@ -718,40 +718,6 @@
     fi
     AS_IF([test "x$enable_hyperscan" = "xyes"], [AC_DEFINE([BUILD_HYPERSCAN], [1], [Intel Hyperscan support enabled])])
 
-  # libyaml
-    AC_ARG_WITH(libyaml_includes,
-            [  --with-libyaml-includes=DIR  libyaml include directory],
-            [with_libyaml_includes="$withval"],[with_libyaml_includes=no])
-    AC_ARG_WITH(libyaml_libraries,
-            [  --with-libyaml-libraries=DIR    libyaml library directory],
-            [with_libyaml_libraries="$withval"],[with_libyaml_libraries="no"])
-
-    if test "$with_libyaml_includes" != "no"; then
-        CPPFLAGS="${CPPFLAGS} -I${with_libyaml_includes}"
-    fi
-
-    AC_CHECK_HEADER(yaml.h,,LIBYAML="no")
-
-    if test "$with_libyaml_libraries" != "no"; then
-        LDFLAGS="${LDFLAGS} -L${with_libyaml_libraries}"
-    fi
-
-    LIBYAML=""
-    AC_CHECK_LIB(yaml,yaml_parser_initialize,,LIBYAML="no")
-
-    if test "$LIBYAML" = "no"; then
-        echo
-        echo "   ERROR!  libyaml library not found, go get it"
-        echo "   from http://pyyaml.org/wiki/LibYAML "
-        echo "   or your distribution:"
-        echo
-        echo "   Ubuntu: apt-get install libyaml-dev"
-        echo "   Fedora: dnf install libyaml-devel"
-        echo "   CentOS/RHEL: yum install libyaml-devel"
-        echo
-        exit 1
-    fi
-
     LIBHWLOC=""
     AC_ARG_ENABLE(hwloc,
             AS_HELP_STRING([--enable-hwloc], [Enable hwloc support [default=no]]),