OPA Filters: New bundle activation affects the policy decisions

[wisinghe]

Describe the bug
When skipper is serving traffic on a route with an OPA filter, if the OPA filter gets a new bundle version, it will return error decisions for ~0.1 - 0.2% of the traffic.

To Reproduce

1. Have a skipper running with an enabled OPA filter for a route.
2. Put traffic on the route (at least 500rps)
3. Trigger a bundle update by updating the policy bundle in the bundle server.
4. Monitor the response codes for the requests.

Expected behavior
Policy updates should be smooth and should not impact policy evaluations in the runtime.

Observed behavior
Updating policies cause decision error.