Add meta tag helper for trace propagation to Django.

[AbhiPrasad]

Add sentry_trace() template helper for Django

We should make it easy to add sentry trace meta header OOB in Django. See feedback: #1171

Similar to work done in #1336

EDIT(neel): just start injecting the meta tags automatically

[pickfire]

There is now trace_propagation_meta to help for this #1171, probably need to add a middleware for sentry.

[antonpirker]

Yes, to solve this issue we just need to inject the result of trace_propagation_meta() into Django responses.

Maybe this can be done in here: https://github.com/getsentry/sentry-python/blob/master/sentry_sdk/integrations/django/views.py#L32-L38

Want to give it a go @pickfire ?

[pickfire]

Sorry, I am not interested in working on this myself, given that it's already working for us using the long way.

[antonpirker]

Hey @pickfire

It's fine if you do not want to work on it.
Internernally we will work on something in the next couple of weeks, where we will this feature here, so I guess it will be solved soonish.

[sentrivana]

Closing in favor of #2186