feat: provide a mechanism to temporarily disable aggregation

[eelkevdbos]

For an import job, I would like to disable the aggregation temporarily to improve performance and reduce the risk of deadlocks.

A context manager seems like a suitable interface for such a feature, like so:

with aggregations_disabled():
  # trigger model inserts / updates without triggering aggregation
  ...

A quick and dirty way would be to add (actually, prepend) a line to construct_aggregate_queries like so:

def construct_aggregate_queries(self):
  if self.aggregation_disabled:
    return
  ...

The context manager then implemented like:

@contextmanager
def aggregations_disabled():
  manager.aggregation_disabled = True
  yield
  manager.aggregation_disabled = False

@kvesteri, do you have any thoughts on feasibility of this approach? I'm happy to submit a PR for the feature.