Tree viewset for retrieving nested, paginated views of topic trees

[rtibbles]

Summary

• To accommodate the nested, paginated topic tree display as outlined in designs for this feature: Implement categorical and primary metadata search kolibri-ecosystem#7 this PR creates an API endpoint that allows for subsections of a topic tree to be queried in a single request, with the parent node, the paginated children, and the paginated grand children.
• The children and the children of each child are returned as a pagination object, containing the results Array, and more which is either null or an object with the parameters that can be passed to the same endpoint in order to query for more results.
• This PR also updates the ContentNodeResource to allow for simple access to the tree endpoint without having to define a new resource, and with a simplified caching mechanism that works across the TreeViewset and ContentNodeViewset requests.

References

Fixes #8108

Contributes to the solution for #7525

I did a dummy implementation using the current topics page as a PoC of using this API, an animation is seen here, but I did not commit the changes for this:

Reviewer guidance

Does the API and its tests make sense?
Are the changes to the ContentNodeResource a good model for handling read only resources in the future?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[nucleogenesis]

Just a couple requests for comments in the contentNode.js otherwise it looks good to me.

[nucleogenesis]

EDIT: - With this branch off of this PR's branch checked out I saw completely solid response times and payloads 👍

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I'm also getting 30+ second loading times and every payload coming back is precisely 16.7MB.

I can't even view the response from the server because it freezes the browser tab.

[jredrejo]

Just a couple of minor details. Overall it looks great

Comments addressed.

[jredrejo]

Thank you, I see it good to go.