Use Redis for sequence token

[aodhan-domhnaill]

See logstash-plugins/logstash-input-couchdb_changes#50

[njuguna-n]

This merged PR offers an alternative way of keeping track of the sequence token. I will follow up with the PR Aidan linked in the description but it it is not as urgent given the work around. We will need to make sure we add a similar config to our Kubernetes configs.

[andrablaj]

Closing this issue as we are not considering using Redis anymore.