@brief Extend the list of edge definitions to construct a graph.

`graph_module._extendEdgeDefinitions(edgeDefinitions, relation1, relation2, ..., relationN)`

In order to add more edge definitions to the graph before creating
this function can be used to add more definitions to the initial list.

@PARAMS

@PARAM{edgeDefinitions, array, required}
A list of relation definition objects.

@PARAM{relationX, object, required}
An object representing a definition of one relation in the graph

@EXAMPLES

@EXAMPLE_ARANGOSH_OUTPUT{generalGraphEdgeDefinitionsExtend}
  var graph_module = require("@arangodb/general-graph");
  directed_relation = graph_module._relation("lives_in", "user", "city");
  undirected_relation = graph_module._relation("knows", "user", "user");
  edgedefinitions = graph_module._edgeDefinitions(directed_relation);
  edgedefinitions = graph_module._extendEdgeDefinitions(undirected_relation);
@END_EXAMPLE_ARANGOSH_OUTPUT