API does not handle absence of tags / blocklist service gracefully

For reference, the implementation of the service can be found here: https://github.com/InetIntel/grip-core/tree/master/grip/tagger/tags

If this service is unavailable, the API fails to return any events at all. It would probably be more user-friendly if we found a way to carry on without the info provided by this service.

For example, if the query for the blocklist fails, just proceed with an empty blocklist. If the query for the tag information fails, we could use a placeholder instead.

Start by tracing the API's integration with the tag service described at grip/tagger/tags and identify where unavailable blocklist or tag queries cause event handling to fail. Add coverage for service failures, then verify that events still return with an empty blocklist or placeholder tag information as appropriate.

Written by the indexing model from the issue text.