Allow Zipkin to write to an Elasticsearch alias, without date, making ILM possible

Feature

Elasticsearch can manage the indices itself now via ILM, so it would make sense to let Zipkin write to an alias instead and letting Elastisearch handle rotation and retention.

Rationale

More flexibility in managing your data in ELK and the possibility to utilize Elastisearchs ILM feature.

Example Scenario

Users that have a very large set of tracing data can then choose a shorter rollover period.
Not just them, but it's just more manageable overall.