ES|QL: Add TBUCKET function

Replace evaluation by a surrogate.

Closes #131068

Author: leontyevdv

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/grouping/TBucketTests.java

@@ -31,6 +31,7 @@
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasSize;
 
+// TODO: WIP
 public class TBucketTests extends AbstractAggregationTestCase {
     public TBucketTests(@Name("TestCase") Supplier<TestCaseSupplier.TestCase> testCaseSupplier) {
         this.testCase = testCaseSupplier.get();