[TASK] Describe migrating assets to public/_assets

[garvinhicking]

Mostly taken from the improved ChangeLog of the TYPO3 core, with some Sphinx-rendering adaptations and a crosslink.

Exact differences from the merged Changelog https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/12.0/Important-98484-ExtensionsOutsideOfDocumentRootForComposer-basedTYPO3Installations.html#important-98484-1664553704 are:

• Use ":html:" instead of ":fluid:" (does not exist in Sphinx)
• Use ":html:" instead of ":css:" (doesn ot exist in Sphinx)
• Reference the "cms-composer-installers" Link
• Refrence helhum/typo3-console
• Reference ChangeLog entry
• Remove "impact" headline, use "migration" instead. Add a paragraph with a short intro.

Once this is merged, we can link to it from:

https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/ApiOverview/DirectoryStructure/Index.html#file-public-assets

References https://github.com/TYPO3-Documentation/Changelog-To-Doc/issues/920

Releases: main, 12.4

[linawolf]

I switched to the new rendering, so you can rebase and apply the needed changes right away.

[brotkrueml]

Will have a look, but not today.

[garvinhicking]

@brotkrueml Thank you; yes, I already planned to wait for you before merging. Take your time - I'll rebase this to new rendering first then, as well.

[github-actions[bot]]

The backport to 12.4 failed:

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

stderr

``` error: could not apply bcde076... [TASK] Describe migrating assets to public/_assets hint: After resolving the conflicts, mark them with hint: "git add/rm ", then run hint: "git cherry-pick --continue". hint: You can instead skip this commit with "git cherry-pick --skip". hint: To abort and get back to the state before "git cherry-pick", hint: run "git cherry-pick --abort". hint: Disable this message with "git config advice.mergeConflict false" ```

stdout

``` CONFLICT (modify/delete): Documentation/Settings.cfg deleted in HEAD and modified in bcde076 ([TASK] Describe migrating assets to public/_assets). Version bcde076 ([TASK] Describe migrating assets to public/_assets) of Documentation/Settings.cfg left in tree. ```

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-12.4 12.4
# Navigate to the new working tree
cd .worktrees/backport-12.4
# Create a new branch
git switch --create backport-379-to-12.4
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick bcde0768cc3d4c90cf252a04e9d15c51fc47ee3e,d34fb581e746902ac8338ce690ef7663c2801939,a9b1f71d2558bd33171acb32d0dd65fc760ad038
# Push it to GitHub
git push --set-upstream origin backport-379-to-12.4
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-12.4

Then, create a pull request where the base branch is 12.4 and the compare/head branch is backport-379-to-12.4.