Add comment to EsqlProject

Author: alex-spies

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/logical/local/EsqlProject.java

@@ -21,6 +21,10 @@
 import java.io.IOException;
 import java.util.List;
 
+/**
+ * A projection when first parsed, i.e. obtained from {@code KEEP, DROP, RENAME}. After the analysis step, we use {@link Project}.
+ */
+// TODO: Can this be consolidated with Project? We don't need the pre-/post-analysis distinction for other logical plans.
 public class EsqlProject extends Project {
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(
         LogicalPlan.class,