Remove leak of entire variableContent on variable validation.

[Sam-tesouro]

RELATED cosmo-issues-1182

Currently if a request fails variable validation via renderVariableRequiredNotProvidedError or renderVariableInvalidObjectTypeError the entire variable content is dumped onto the message which then makes it's way onto telemetry as statusMessage regardless of any compliance settings.

This is less then ideal from a compliance perspective because there may be sensitive information leaked that we have no reason to believe is malformed. It makes the complexity of adhering to PII regulations such as PCI more challenging.

A simple solution would be to simply remove the variable content from the message. I would be more then happy to make this change and update relevant tests if y'all believe this is worthwhile.

I see there is also already a secondary mechanism on Cosmo by which you could add export variables as trace attributes (TRACING_EXPORT_GRAPHQL_VARIABLES) so I believe this change has very limited demerits.

Proposed change

func (v *variablesVisitor) renderVariableInvalidObjectTypeError(typeName []byte, variablesNode astjson.Node) {
	out := &bytes.Buffer{}
	err := v.variables.PrintNode(variablesNode, out)
	if err != nil {
		v.err = err
		return
	}
	v.err = &InvalidVariableError{
		Message: fmt.Sprintf(`Variable "$%s" got invalid value; Expected type "%s" to be an object.`, string(v.currentVariableName), string(typeName)),
	}
}

func (v *variablesVisitor) renderVariableRequiredNotProvidedError(fieldName []byte, typeRef int) {
	out := &bytes.Buffer{}
	err := v.variables.PrintNode(v.variables.Nodes[v.currentVariableJsonNodeRef], out)
	if err != nil {
		v.err = err
		return
	}
	out.Reset()
	err = v.definition.PrintType(typeRef, out)
	if err != nil {
		v.err = err
		return
	}
	v.err = &InvalidVariableError{
		Message: fmt.Sprintf(`Variable "$%s" got invalid value; Field "%s" of required type "%s" was not provided.`, string(v.currentVariableName), string(fieldName), out.String()),
	}
}

[jensneuse]

I've responded in the corresponding issue on the cosmo repo.