Raise an error when a missing contract is specified to read-storage

[UsmannK]

Before:

$ slither-read-storage 0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2 --contract-name WETH8 # woops! did you mean WETH9?
$ # silently fails

After

$ slither-read-storage 0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2 --contract-name WETH8
Traceback (most recent call last):
  File "/Users/usmannkhan/Development/slither/env/bin/slither-read-storage", line 8, in <module>
    sys.exit(main())
  File "/Users/usmannkhan/Development/slither/slither/tools/read_storage/__main__.py", line 134, in main
    raise SlitherError(f"Contract {args.contract_name} not found.")
slither.exceptions.SlitherError: Contract WETH8 not found.