Enhancement Request: allowOverwrite option + confirmation for duplicate uploads

[ewrayjohnson]

Summary
The upload UI currently blocks duplicate filenames client‑side, preventing server‑side overwrite workflows (e.g., versioning systems, audit trails, WebDAV). Add a configuration option to allow duplicates with user confirmation, while defaulting to the current blocking behavior when the option is not set.

Current behavior (blocking)
In frontend/src/FileManager/Actions/UploadFile/UploadFile.action.jsx , the checkFileError function rejects duplicate filenames::

const fileExists = currentPathFiles.some(
  (item) => item.name.toLowerCase() === file.name.toLowerCase() && !item.isDirectory
);
if (fileExists) return t("fileAlreadyExist");

Result: User cannot upload a file with the same name as an existing file, even if the backend supports overwrite.

Requested behavior
Add a config flag to fileUploadConfig:

<FileManager
  ...
  fileUploadConfig={{ allowOverwrite: true }}
/>

Logic:

1. Default behavior remains unchanged (duplicates are blocked)
2. If allowOverwrite is true:
   -- show a confirmation prompt when duplicate name is detected
   -- if user confirms → proceed with upload
   -- if user cancels → abort upload

Pseudo‑code:

if (fileExists) {
  if (!_allowOverwrite_) return t("fileAlreadyExist");
  const confirmed = window.confirm(t("confirmOverwrite"));
  if (!confirmed) return t("uploadCanceled");
}

Rationale
Backends with versioned storage, audit trails, or WebDAV require overwrites to be handled server‑side:

• Example: REST API with overwrite=true header creates UPDATE audit entries (not DELETE + CREATE)
• Example: WebDAV PUT operations with precondition headers manage versions
• Current limitation: Client blocks the upload before server can decide
  This enhancement allows backends to implement proper versioning while maintaining safe defaults for traditional file managers.

Acceptance criteria

• No config provided → identical behavior to today (blocks duplicates)
• allowOverwrite: true → duplicate filename triggers confirmation dialog
• User confirms → upload proceeds normally
• User cancels → upload aborted (no error message, just silent cancellation)
• Existing code paths unaffected
• Tests updated for both code paths

i18n additions

{
  "confirmOverwrite": "A file with this name already exists. Do you want to replace it?",
  "uploadCanceled": "Upload canceled."
}