Upload event cover picture

[indcoder]

Fixes #85

Add functionality to upload event cover picture to Cloudinary in ScheduleEvent.razor.

• Frontend Changes:

  • Add a file input element for uploading the event cover picture in ScheduleEvent.razor.
  • Integrate Cloudinary's signed upload functionality directly from the web frontend.
  • Inform the user of the image upload restrictions as outlined by Cloudinary.
  • Update the HandleValidSubmit method to include the cover picture upload logic.
  • Add a new property CoverPicture of type string in Event.cs to store the URL of the uploaded cover picture.
  • Add a new method UploadCoverPicture in IEventService.cs to handle the cover picture upload logic.
  • Implement the UploadCoverPicture method in EventService.cs to handle the cover picture upload logic using Cloudinary's signed upload functionality.

• Backend Changes:

  • Add a reference to the backend node.js project for signature generation in Program.cs.
  • Pass the Cloudinary config from the AppHost level to the node.js project resource.
  • Create the nodejs project resource and pass the Cloudinary configs to it.

• Node.js Project:

  • Create a new backend node.js project for signature generation in services/CloudinaryImageSigning/app.js.
  • Implement the signature generation logic using Cloudinary's API.
  • Add a configuration file for the backend node.js project to store Cloudinary account details in services/CloudinaryImageSigning/config.js.

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