V15: Client should validate maxFileSize and allowed/disallowed file types from server configuration

[iOvergaard]

Description

Fail early if file upload exceeds certain parameters.

Changes

• Implements the temporary file configuration endpoint with repository, store, and mock data
• Adds validation for maxFileSize in bytes in the TemporaryFileManager to fail early for any field wanting to upload a temporary file (media picker, file upload, RTE, dropzone)
• Adds validation for allowedUploadedFileExtensions and disallowedUploadedFileExtensions based on server settings to fail early for fields uploading temporary files
• Adds a new utility function to format the "bytes" number to a human-readable number.

Caveats

• When uploading a file in the media library dropzone, the client will still ask you to pick a media type even though the file might be invalid. There will be an upcoming pull request adding some validation to the dropzone itself to remedy some of this.

How to test

1. Set the server configuration Runtime::MaxRequestLength to something like 51200 (50 MB) and try to upload an image larger than that. It should now warn you that the image is too large in the media picker, RTE, media library, etc, and it should NOT make a server request.
2. Set the server configuration Content::DisallowedUploadedFileExtensions to something like ["exe"] and try to upload a .exe file, check that a warning is shown to the user and NO request is sent.
3. Check that the opposite of the above is true, i.e., you can upload allowed files

[leekelleher]

Tested out, working great! 🚀