Request URLs for bundled create requests should allow a leading "/" on the url field

[jecihjoy]

From the issue raised here where a bundle with request urls having a leading "/" throws a non clear exception;

The error
"text": "Request URL for bundled create requests should have a path with exactly one token (<resourceType>)."
might not be descriptive enough

Suggesting that either

1. To allow both "url": "/Observation" and "url": "Observation" to work
2. Or, to throw a clear exception