Add option to conditionally use signals in Django

[vladanpaunovic]

Make it possible for users to enable/disable the span generation for Django signals. In some projects there can be hundreds of signals be triggered with each request, this leads to a lot of noise in the UI and also possibly to data truncation because the payload of an event grows to big and then maybe important data is lost.

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[sentrivana]

To turn off span creation for all signals, use signals_spans=False: https://docs.sentry.io/platforms/python/integrations/django/#options

There's a community PR to introduce a more granular denylist which we'll review soon.