chore: add gevent as bundle dependency

[Ian2012]

Description

Adds gevent as a bundle dependency to optimize celery for I/O bound tasks when running multiple queues.

By itself this change will not affect Celery, to work you need to change the pool option from process to gevent and increase the concurrency parameter. This parameter is currently not set by tutor and shouldn't reflect any change on their installations unless it's specifically changed.

For more information on the Celery's pool option: https://celery.school/celery-worker-pools

The technical details can be found here: overhangio/tutor#1130

Supporting information

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Testing instructions

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Deadline

None

Other information

See openedx/openedx-aspects#116 (comment) for more information

[felipemontoya]

@Ian2012 it took me a while to get to this as I did not understand the product requirement. Now, when reviewing the context links I found:

we have developed a tutor Celery plugin to manage multiple queues for Celery. With it, we have tested switching to a gevent pool which uses lightweight threads on the default lms worker deployment with concurrency set to 100 events. It improved a lot the performance of the tasks.

This raises so many questions for me:

• How much is a lot of performance gains?
• how many events/second (or any other meassure of traffic that you have studied) can regular celery handle before this 'gevent' package is needed?
• is the eduNEXT/tutor-contrib-celery plugin obligatory for aspects?
• Is technically possible to add this dependency from the tutor-celery-plugin?
• will this only affect installs that are running aspects?

I think adding a new dependency, specially one that is fixed in code, but will be using in operations only is weird. The natural place for the dependency would be the actual plugin that uses the code. Even if this needs to be present in the edxapp image perhaps we should move it to openedx/platform-plugin-aspects.