Support content renderable_only option in tasks API

[dbnicholson]

This is the last non-backend specific option to allow the tasks API to have the same interface as the CLI.

Summary

I wanted to make an API request to import content with renderable_only=False (equivalent to --include-unrenderable-content), but that's not in the API.

References

Similar to #10229.

Reviewer guidance

Create a homedir and provision the facility with a superuser. Then run the server with --settings kolibri.deployment.default.settings.dev so it accepts HTTP Basic authentication. Then you can trigger a content import like:

curl -u "$user:$password" -H 'Content-Type: application/json' -d '{"type": "kolibri.core.content.tasks.remotecontentimport", "channel_id": "$some_channel_id", "channel_name": "something", "renderable_only": false}' http://127.0.0.1:8080/api/tasks/tasks/

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Testing checklist

• Contributor has fully tested the PR manually
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PR process

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Reviewer checklist

• Automated test coverage is satisfactory
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• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
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[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0b7.dev0_git.17.g48424aad.pex
Windows Installer (EXE)	kolibri-0.16.0b7.dev0+git.17.g48424aad-unsigned.exe
Debian Package	kolibri_0.16.0b7.dev0+git.17.g48424aad-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0b7.dev0+git.17.g48424aad-0.3.0.dmg
Android Package (APK)	kolibri-0.16.0b7.dev0+git.17.g48424aad-0.1.0-debug.apk
TAR file	kolibri-0.16.0b7.dev0+git.17.g48424aad.tar.gz
WHL file	kolibri-0.16.0b7.dev0+git.17.g48424aad-py2.py3-none-any.whl

[bjester]

Looks good to me. @rtibbles ?

[rtibbles]

Seems fine to me - although this flag has always been of rather limited use!