Add hook to set custom span name in django instrumentation

[lzchen]

Similar to wsgi, accept a callback function in DjangoInstrumentor().instrument to be able to pass custom span name.

The specs say "MAY" for this feature, but we should be consistent across our instrumentations.

Part of open-telemetry/opentelemetry-python#1297

[NickSulistio]

I can take on this issue! @NickSulistio

cc @alolita

[owais]

@NickSulistio I added request/response hooks to Django instrumentation. They can be used to set span name (among other things) on the server span. I think adding a special hook just for span name would be redundant after these changes. Sorry about not notifying you earlier about this.

Good news is that we need similar request/response hooks for all web server instrumentations such as flask, falcon, tornado etc and you can implement that if you'd like. Let me know if that's interesting to you and we can discuss it.

[owais]

More details: #408

[NickSulistio]

Hi @owais, do you think that these would be good first issues? This is the first time I'm contributing to an open source project, so I think that if this issues are not too complicated then I would be willing to take them!

[owais]

Yes, they're the same complexity as the span name callback was. They're very similar actually. Feel free to ping me on slack if you need help with anything.