Add file type check to form type file (key: allowedFileTypes)

[Phocacius]

Adds a file extension check to uploaded files. The configuration key is allowedFileTypes. It expects a comma-separated list of allowed extensions (ignoring case). If unset, all files are allowed (as it was before).

Example config:

-
  type: file
  text: 'Upload an image'
  name: image
  allowedFileTypes: 'jpeg, jpg, png'

⚠️ Only the filename extension is checked, not the actual content.

[Copilot]

Pull request overview

This PR adds file type validation for file uploads in forms by introducing a new allowedFileTypes configuration option. The validation is based on file extension matching (case-insensitive) and displays translated error messages when invalid file types are uploaded.

• Implements client-side file extension validation using the allowedFileTypes configuration key
• Adds error message translations across 11 languages for invalid file type feedback
• Updates JavaScript to use modern const declarations and arrow functions

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

File	Description
src/Mapbender/DataManagerBundle/Resources/public/FormRenderer.js	Implements file extension validation logic and updates variable declarations to const
src/Mapbender/DataManagerBundle/Resources/translations/messages.*.yaml	Adds "invalid_file_extension" error message translations for 11 languages
CHANGELOG.md	Documents the new feature addition

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[astroidex]

• tested. works fine