Export random sampler agg from server (#104747)

The server module exports the classes needed to use most
aggregations, but the random sampler aggregation was missed.
(I think it's because the PRs to add random sampler and to
add modularization in general were both long-running and were
in flight around the same time.) This PR adds an export for
the random sampler agg, so that it can be used from plugins.

server/src/main/java/module-info.java

@@ -333,6 +333,7 @@ module org.elasticsearch.server {
     exports org.elasticsearch.search.aggregations.bucket.nested;
     exports org.elasticsearch.search.aggregations.bucket.range;
     exports org.elasticsearch.search.aggregations.bucket.sampler;
+    exports org.elasticsearch.search.aggregations.bucket.sampler.random;
     exports org.elasticsearch.search.aggregations.bucket.terms;
     exports org.elasticsearch.search.aggregations.bucket.terms.heuristic;
     exports org.elasticsearch.search.aggregations.metrics;