[Fixes #12229] tinymce is not visible after the upgrade to v4

[mattiagiupponi]

Checklist

Reviewing is a process done by project maintainers, mostly on a volunteer basis. We try to keep the overhead as small as possible and appreciate if you help us to do so by completing the following items. Feel free to ask in a comment if you have troubles with any of them.

For all pull requests:

• Confirm you have read the contribution guidelines
• You have sent a Contribution Licence Agreement (CLA) as necessary (not required for small changes, e.g., fixing typos in the documentation)
• Make sure the first PR targets the master branch, eventual backports will be managed later. This can be ignored if the PR is fixing an issue that only happens in a specific branch, but not in newer ones.

The following are required only for core and extension modules (they are welcomed, but not required, for contrib modules):

• There is a ticket in https://github.com/GeoNode/geonode/issues describing the issue/improvement/feature (a notable exemption is, changes not visible to end-users)
• The issue connected to the PR must have Labels and Milestone assigned
• PR for bug fixes and small new features are presented as a single commit
• Commit message must be in the form "[Fixes #<issue_number>] Title of the Issue"
• New unit tests have been added covering the changes, unless there is an explanation on why the tests are not necessary/implemented
• This PR passes all existing unit tests (test results will be reported by travis-ci after opening this PR)
• This PR passes the QA checks: black geonode && flake8 geonode
• Commits changing the settings, UI, existing user workflows, or adding new functionality, need to include documentation updates
• Commits adding new texts do use gettext and have updated .po / .mo files (without location infos)

Submitting the PR does not require you to check all items, but by the time it gets merged, they should be either satisfied or inapplicable.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.01%. Comparing base (ffde050) to head (58d69b6).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #12230   +/-   ##
=======================================
  Coverage   64.01%   64.01%           
=======================================
  Files         870      870           
  Lines       52221    52221           
  Branches     6487     6487           
=======================================
  Hits        33431    33431           
  Misses      17289    17289           
  Partials     1501     1501           

[github-actions]

The backport to 4.3.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-4.3.x 4.3.x
# Navigate to the new working tree
cd .worktrees/backport-4.3.x
# Create a new branch
git switch --create backport-12230-to-4.3.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 73055bde345622d4c12abb3ebc2e3eec7750d191
# Push it to GitHub
git push --set-upstream origin backport-12230-to-4.3.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-4.3.x

Then, create a pull request where the base branch is 4.3.x and the compare/head branch is backport-12230-to-4.3.x.