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.
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