Support ElasticSearch for Log Storage with Delegated Forwarding

[adambkaplan]

Feature request

Allow Tekton Results to use ElasticSearch as the log storage backend, with log forwarding delegated to Fluentd or equivalent.

Use case

Many production clusters are already configured to forward application logs to ElasticSearch via Fluentd. Log forwarding via Tekton Results would be redundant in this scenario. Delegating log forwarding also can improve scalability, as these tools are designed to stream logs generically.