Returns the mime-type of a binary and optionally a normalized file-name.
@spec file_mime_type(String.t()) :: {:ok, String.t()} | {:error, :unknown_mime}
@spec file_mime_type(String.t(), String.t()) :: {:ok, content_type :: String.t(), filename :: String.t()} | {:error, :unknown_mime | :failed_to_fix_extension}