fix: legacy node data without best_block property

[alexruzenhack]

Acceptance Criteria

• Fix by making the best_block property Optional.

Log of the error:

[ERROR] MissingValueError: missing value for field "nodes.best_block"
Traceback (most recent call last):
  File "/var/task/handlers/node_data_aggregator.py", line 10, in handle
    result_aggregate = aggregate_node_data.aggregate()
  File "/var/task/usecases/aggregate_node_data.py", line 39, in aggregate
    old_network = self.node_gateway.get_network()
  File "/var/task/gateways/node_gateway.py", line 111, in get_network
    return Network.from_dict(value)
  File "/var/task/domain/network/network.py", line 214, in from_dict
    return from_dict(
  File "/opt/python/dacite/core.py", line 63, in from_dict
    value = _build_value(type_=field.type, data=transformed_value, config=config)
  File "/opt/python/dacite/core.py", line 90, in _build_value
    return _build_value_for_collection(collection=type_, data=data, config=config)
  File "/opt/python/dacite/core.py", line 140, in _build_value_for_collection
    return data_type(_build_value(type_=item_type, data=item, config=config) for item in data)
  File "/opt/python/dacite/core.py", line 140, in <genexpr>
    return data_type(_build_value(type_=item_type, data=item, config=config) for item in data)
  File "/opt/python/dacite/core.py", line 92, in _build_value
    return from_dict(data_class=type_, data=data, config=config)
  File "/opt/python/dacite/core.py", line 75, in from_dict
    raise MissingValueError(field.name)

Security Checklist

• [x] Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.