Restrict file extension / mime type for file drop share

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Is your feature request related to a problem? Please describe.
I want to share a folder a give the recipients the option to upload files. However, there are often cases where I want to limit the allowed file types one may upload. E.g. only allow PDF instead of .docx and .md, or allow all image/* and video/* mime types but not anything else.

Describe the solution you'd like
The customized link option should also provide the option to limit the file extension and mime type. These should be checked server-side, and also set on the upload dialog client-side to preset the correct filter in the browsers native file selection dialog.

Describe alternatives you've considered

Additional context

Start by tracing the customized-link file upload flow in the Nextcloud server, including the upload dialog and its server-side handling. Identify the relevant entry points before adding extension and MIME-type restriction support; done means permitted types are enforced by the server and applied to the browser's file-selection filter.