Add support for disabling feature datasets (#6666)

This change adds support for disabling datasets, such that specific
files are not loaded into memory when running OSRM. This enables users
to not pay the memory cost for features they do not intend to use.

Initially, there are two options:
- ROUTE_GEOMETRY, for disabling overview, steps, annotations and waypoints.
- ROUTE_STEPS, for disabling steps only.

Attempts to query features for which the datasets are disabled will
lead to a DisabledDatasetException being returned.

include/osrm/datasets.hpp

@@ -0,0 +1,15 @@
+#ifndef DATASETS_HPP
+#define DATASETS_HPP
+
+namespace osrm::storage
+{
+
+enum class FeatureDataset
+{
+    ROUTE_STEPS,
+    ROUTE_GEOMETRY,
+};
+
+} // namespace osrm::storage
+
+#endif

include/osrm/error_codes.hpp

@@ -23,7 +23,8 @@ enum ErrorCode
     FileIOError,
     UnexpectedEndOfFile,
     IncompatibleDataset,
-    UnknownAlgorithm
+    UnknownAlgorithm,
+    UnknownFeatureDataset
 #ifndef NDEBUG
     // Leave this at the end.  In debug mode, we assert that the size of
     // this enum matches the number of messages we have documented, and __ENDMARKER__