fix(filer.meta.tail): error instead of silently dropping events when -es is used without elastic build tag
The default chrislusf/seaweedfs image builds without the `elastic` build
tag, so sendToElasticSearchFunc was a no-op that returned a function
discarding every event. Users passing -es saw the subscription wire up
in filer logs but nothing ever reached Elasticsearch.
Return an error explaining the binary wasn't built with ES support and
pointing at the build flag. The caller already prints the error and
exits, so users now get an immediate, actionable message.
Fixes#9190
Chris Lu