fix(upload): handle invalid file type error and improve MIME type handling

[Ivan-Shaml]

(Prerequisite: podkrepi-bg/api#700)

Currently the API supports an allow list for mime types and file extensions, for all the endpoints which support file upload.

However the front-end lacks in this area:

• If file upload fails, on many places appropriate message, is not shown to the user
• We know the supported mime types, but don't enforce them on the FileUpload component. This creates a gap, where user can upload unsupported file format and create an error.

Motivation and context

Continuation of podkrepi-bg/api#700
Trying to improve the UX of users when uploading files.

Screenshots:

Before	After

Testing

Steps to test

(Prerequisite: need to be running this version of the API podkrepi-bg/api#700)

1. Add file type to the allow list (e.g. application/x-msdownload) in FileUpload.tsx
2. Upload an exe file
3. See the error notification

Affected urls

• http://localhost:3040/admin/campaigns/create
• http://localhost:3040/admin/campaigns/edit/{campaignId}
• http://localhost:3040/admin/irregularities
• http://localhost:3040/admin/irregularities/{id}
• http://localhost:3040/admin/expenses/create
• http://localhost:3040/admin/expenses/{id}
• http://localhost:3040/admin/campaign-news/edit/{id}
• http://localhost:3040/admin/campaign-news/create

Environment

New environment variables:

None

New or updated dependencies:

None

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