Misc smaller patch release fixes for v2023.07.05

[bjester]

Summary

Description of the change(s) you made

• Made the Channel Details component defensive against missing keys, by using lodash' defaultsDeep and a sensible defaults object
• Prevented access to channel.deleted in the admin's version of channel details if channel isn't yet defined
• Added mappings for ZIM content kind to places where we enumerate settings and values for other content kinds
• Added defensive check against the only .icon property access
• Added kolibri_placeholder.png image that was expected to exist when generating PDFs for a channel that has imported content from a channel without a thumbnail
• Fixes undocumented issue in the Admin section where a component was accessing an undefined template variable

Manual verification steps performed

For #4193 and #4194

1. Edited get_channel_details endpoint to pop some details keys like categories and levels
2. Loaded the channel details
3. Observed no errors and that the keys were indeed missing in the response

For #4195

1. Opened Administration section
2. Viewed a channel's details
3. Observed no errors

For #4200

1. Opened a channel for editing
2. Navigated around
3. Observed no errors related to changes
4. Navigate to Settings > Storage
5. Observe the ZIM type has an icon (missing string referenced here)

For #4206

1. Opened channels list in the Administration section
2. Clicked ACTIONS on a channel which has imported content from another channel without a thumbnail
3. Clicked 'Download PDF'
4. Observed the PDF was generated and downloaded appropriately

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Reviewer guidance

How can a reviewer test these changes?

The above manual steps

References

Fixes #4193
Fixes #4194
Fixes #4195
Fixes #4200
Fixes #4206

Comments

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Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
• If this includes an internal dependency change, a link to the diff is provided
• The docs label has been added if this introduces a change that needs to be updated in the user docs?
• If any Python requirements have changed, the updated requirements.txt files also included in this PR
• Opportunities for using Google Analytics here are noted
• Migrations are safe for a large db

Studio-specifc:

• All user-facing strings are translated properly
• The notranslate class been added to elements that shouldn't be translated by Google Chrome's automatic translation feature (e.g. icons, user-generated text)
• All UI components are LTR and RTL compliant
• Views are organized into pages, components, and layouts directories as described in the docs
• Users' storage used is recalculated properly on any changes to main tree files
• If there new ways this uses user data that needs to be factored into our Privacy Policy, it has been noted.

Testing:

• Code is clean and well-commented
• 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
• Any new interactions have been added to the QA Sheet
• Critical and brittle code paths are covered by unit tests

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Reviewer's Checklist

This section is for reviewers to fill out.

• 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

[marcellamaki]

Thanks @bjester - this looks good to me after code review, and all of the manual QA steps you have listed here check out.