18896 Replace STORAGE_BACKEND with STORAGES and support Script running from S3

[arthanson]

Fixes: #18896 (and #18423)

This Allows scripts to be run from S3 as well as config changes to allow for setting it. The changes are in two basic parts - the Script Form is changed to upload files using Django-storages (either FileSystem or S3) and the Script module loader is changed to pull from Django-storages.

• Django-storages is now a requirement
• STORAGE_BACKEND is now deprecated
• STORAGES is now set directly as a config option
• write_to_disk was moved from DataFile to ManagedFile as it is only ever used there or in classes derived from it.
• The changes in BaseScript find_source is a replacement for the inspect module to actually find and load the modules.
• extras.storage.ScriptFileSystemStorage is required for backwards compatibility with SCRIPTS_ROOT setting as otherwise with normal FileSystemStorage it will cause a path permission error going outside media root.

Note: the Script convenience methods load_yaml and load_json are not compatible when using S3 as they go direct to the local file system and are based on the path of the Script so wouldn't be backwards compatible. They are convenience functions so the script author could write them directly.

RELEASE_NOTES should probably have a section about replacing STORAGE_BACKEND and STORAGE_CONFIG with STORAGES for those updating from a previous version.

[jeremystretch]

Looking good! Found a few things I think we can clean up.

[jeremystretch]

@arthanson could you submit a retroactive FR for this work please? The scope of #18423 was just the configuration parameter change. The changes here have a far broader impact (such as introducing django-storages as a new mandatory dependency) that need to be captured.

[jeremystretch]

Thanks @arthanson!

[jeremystretch]

This still needs a corresponding FR which captures the full extent of changes made in the PR. #18423 is not sufficient for this in its current form.

[arthanson]

This still needs a corresponding FR which captures the full extent of changes made in the PR. #18423 is not sufficient for this in its current form.

Expanded the issue with more details. Please let me know if there are any details missing or how it should be expanded if needed.

[jeremystretch]

@arthanson please revert your edits to #18423 and open a new feature request to capture the intent of this PR, and re-target this PR to the new FR. I opened #18423 solely to propose a change to the configuration parameters in use. I'm not comfortable having it appear as though I requested this change; my involvement in this work has been limited to reviewing the proposed changes at a technical level.

[arthanson]

Created issue #18896