celery: use python dict instead of string as attribute value to enable parsing

[shivanshuraj1333]

Fixes: #3169

[xrmx]

I think this does match with the value an attributes can have https://opentelemetry.io/docs/concepts/signals/traces/#attributes

[shivanshuraj1333]

Yes, I opened this and realized that it is intentional.

Right now, since we do value = str(value) the map becomes tricky to parse (filtering based on key).

How about if I flatten the map and then stringily (or convert to corresponding datatype) the values?

celery.delivery_info ⇒ `{'exchange': '', 'routing_key': 'distilled-guidance-dpo-25-10k-v1', 'priority': 0, 'redelivered': False}`

would become

celery.delivery_info.exchange: "routing_key"
celery.delivery_info.routing_key: "distilled-guidance-dpo-25-10k-v1"
celery.delivery_info.priority: 0
celery.delivery_info.redelivered: false

[xrmx]

Flattening the map would indeed be better I think than going out of spec :)

[shivanshuraj1333]

I have updated the changes to add span attributes with flattened map. PTAL, thanks!