Update example for Django 4.2 storage settings

[jacobtylerwalls]

brief description of changes

DEFAULT_FILE_STORAGE was deprecated in Django 4.2, which is used in Arches 7.5. Update the docs to avoid suggesting the use of a deprecated setting.

See: https://docs.djangoproject.com/en/4.2/releases/4.2/#custom-file-storages

This box must be checked

• [x] the PR branch was originally made from the base branch

This box should be checked

• [ ] after these changes the docs build locally without error

This box should only be checked you intend to follow through on it (we can do it on our end too)

• [x] I will cherry-pick all commits in this PR into other branches that should have them after this PR is merged (This should only get cherry-picked to 7.5)

[ekansa]

@jacobtylerwalls Thanks! The version 7.5 documentation will start as a branch from the "master" (main) branch. So your PR to update the master branch keeps things nice and simple.