external jwt signer logs address of existingvalue when failing

[dovholuknf]

see https://github.com/openziti/edge/blob/ac5e2e5c2db4bb171ed36568d70710eda985ee7a/controller/persistence/external_jwt_signer_store.go#L137

It's passing existingValue to NewFieldError. NewFieldError takes an interface and when printed, it's just printing the address of existingValue since existingValue is a *string

the value '0xc003c386f0' for 'jwksEndpoint' is invalid

{"error":{"cause":{"code":"UNHANDLED","message":"the value '0xc003c386f0' for 'jwksEndpoint' is invalid: only one of jwksEndpoint or certPem may be defined"},"code":"REFERENCED_ENTITY_NOT_FOUND","message":"REFERENCED_ENTITY_NOT_FOUND","requestId":"uqFQYz9kL"},"meta":{"apiEnrollmentVersion":"0.0.1","apiVersion":"0.0.1"}}