Added context propagation support to celery instrumentation

[owais]

Description

• Adds context propagation to celery instrumentation.
• Updated celery span operation names to include task type and task name.

fixes #862
fixes #876

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Manual tests
• Added unit test
• Updated docker tests

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[codeboten]

Overall this change looks pretty good to me. @owais is this addressing any of the open issues around celery integration? https://github.com/open-telemetry/opentelemetry-python/issues?q=is%3Aissue+is%3Aopen+celery

[owais]

I think it should fix #876 and probably #862 as well. This PR does not fix #970 but it updates the docs to ackowledge the issue and recommends a solution (delayed instantiate tracing in celery workers so each worker gets it's own processor/exporter instance) See "setting up tracing" section and updated code examples in celery docs. @codeboten

[codeboten]

@owais Thanks for updating the description, this is great! Need one more approval. @open-telemetry/python-approvers approvers please take a look

[lzchen]

Add PR link

[owais]

Updated.

[lzchen]

Curious does this need to be implemented for other instrumentations or is this specific to celery (explicit context propagation)?

[owais]

This is very specific to celery.

[lzchen]

@owais

This is very specific to celery.

Can you explain why?

[owais]

Curious does this need to be implemented for other instrumentations or is this specific to celery (explicit context propagation)?

Sorry, I was answering this and confirming that it is specific to celery (celery context propagation) and does not apply to other instrumentations.