Improve error reporting

[medikoo]

1. Ensure that Rest API resolution error is reported as user error (via ServerlessError), so no stack trace is shown by default.

2. Improve formatting of multiline messages

Before:

  Serverless Error ---------------------------------------
 
  Rest API id could not be resolved.
This might be caused by a custom API Gateway configuration.

In given setup stage specific options such as `tracing`, `logs` and `tags` are not supported.

Please update your configuration (or open up an issue if you feel that there's a way to support your setup).

After:

  Serverless Error ---------------------------------------
 
  Rest API id could not be resolved.
  This might be caused by a custom API Gateway configuration.
  
  In given setup stage specific options such as `tracing`, `logs` and `tags` are not supported.
  
  Please update your configuration (or open up an issue if you feel that there's a way to support your setup).