DOUBLE_FORWARD_SLASHES_IN_URL is not a problem for RBAC; need exemption or built-in pattern adjustment

In some data-plane RBAC authoring like https://github.com/Azure/azure-rest-api-specs/blob/2132eeb6ded5dab7a175dd529adcf0ff6e4b5c78/specification/keyvault/data-plane/Microsoft.KeyVault/preview/7.4-preview.1/rbac.json#L38 a double slash is possible because the scope can be "/" but the service - like ARM itself - does handle this case. This 1 error (emitted twice) is most often the only failure we see and we'd like either a way to exempt it, or maybe having the validator check for RBAC usage - either control-plane or data-plane - would be idea for anyone running into this.

/cc @jlichwa @maorleger