Unmute and fix exponential_histogram.LoadFiltered CSV test

[JonasKunz]

Closes #137727.

There was an occasional failure of the bwc tests with the following cause:

[2025-11-07T08:11:41,491][ERROR][o.e.b.ElasticsearchUncaughtExceptionHandler] [test-cluster-2] fatal error in thread [elasticsearch[test-cluster-2][esql_worker][T#4]], exiting java.lang.AssertionError: No value extractor for [EXPONENTIAL_HISTOGRAM] |  
-- | --
at org.elasticsearch.compute.operator.topn.ValueExtractor.extractorFor(ValueExtractor.java:57) |  
at org.elasticsearch.compute.operator.topn.TopNOperator$RowFiller.<init>(TopNOperator.java:180) |  
at org.elasticsearch.compute.operator.topn.TopNOperator.addInput(TopNOperator.java:401) |  
at org.elasticsearch.compute.operator.Driver.runSingleLoopIteration(Driver.java:294) |  
at org.elasticsearch.compute.operator.Driver.run(Driver.java:191) |  
at org.elasticsearch.compute.operator.Driver$1.doRun(Driver.java:428) |  
at [email protected]/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27) |  
at org.elasticsearch.compute.operator.DriverScheduler$1.doRun(DriverScheduler.java:57) |  
at [email protected]/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27) |  
at [email protected]/org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:35) |  
at [email protected]/org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:1076) |  
at [email protected]/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27) |  
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090) |  
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614) |  
at java.base/java.lang.Thread.run(Thread.java:1474)

I think this happened for the following reason:
In #133393 I added the new ES|QL exponential_histogram type alongside with a capability named exponential_histogram.
In follow-up PRs I then only later added support for TopN (#137313) and CSV tests (#137619).

The CSV tests required the exponential_histogram, which means we had some snapshot versions with that capability, but without TopN support. I wasn't aware that when running BWC tests, we have the feature flags on the older versions we test against enabled, which would produce this failure.

This PR fixes this by adding a new capability, making the test depend on that and unmutes the test.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)