Create the drag and drop file upload

[MI6-824]

This is to create the drag and drop file upload component.

This component should:

• Let a user drop in not just one but multiple files at once.
• Restrict the size of the uploaded files
• Restrict the type of uploaded files (e.g. to pdfs, documents etc)
• Include a manual file upload button.
• Save the uploaded files within the component for client access.

[ad9242]

moved back to re-triage as no longer in progress by previous assignee

[MI6-255]

Some early designs for this in Figma