Fix a master->7.x serialization bug (#54429)

`master` wasn't sending `auto_date_histogram`'s
`minimumIntervalExpression` over the wire to `7.x` nodes even though
everything above `7.3` expected it. We never noticed this because we
didn't have any yml tests for `auto_date_histogram` until I added some
in #54161.

Closes #54396

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/330_auto_date_histogram.yml

@@ -25,9 +25,6 @@ setup:
 
 ---
 "basic":
-  - skip:
-      version: " - 7.99.99"
-      reason: BWC test failures https://github.com/elastic/elasticsearch/issues/54396 && waiting for backport https://github.com/elastic/elasticsearch/pull/54379
   - do:
       search:
         body:

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/AutoDateHistogramAggregationBuilder.java

@@ -110,20 +110,6 @@ public class AutoDateHistogramAggregationBuilder
 
     private String minimumIntervalExpression;
 
-    public String getMinimumIntervalExpression() {
-        return minimumIntervalExpression;
-    }
-
-    public AutoDateHistogramAggregationBuilder setMinimumIntervalExpression(String minimumIntervalExpression) {
-        if (minimumIntervalExpression != null && !ALLOWED_INTERVALS.containsValue(minimumIntervalExpression)) {
-            throw new IllegalArgumentException(MINIMUM_INTERVAL_FIELD.getPreferredName() +
-                " must be one of [" + ALLOWED_INTERVALS.values().toString() + "]");
-        }
-        this.minimumIntervalExpression = minimumIntervalExpression;
-        return this;
-    }
-
-
     /** Create a new builder with the given name. */
     public AutoDateHistogramAggregationBuilder(String name) {
         super(name);
@@ -138,6 +124,14 @@ public class AutoDateHistogramAggregationBuilder
         }
     }
 
+    @Override
+    protected void innerWriteTo(StreamOutput out) throws IOException {
+        out.writeVInt(numBuckets);
+        if (out.getVersion().onOrAfter(Version.V_7_3_0)) {
+            out.writeOptionalString(minimumIntervalExpression);
+        }
+    }
+
     protected AutoDateHistogramAggregationBuilder(AutoDateHistogramAggregationBuilder clone, Builder factoriesBuilder,
             Map<String, Object> metaData) {
         super(clone, factoriesBuilder, metaData);
@@ -156,19 +150,24 @@ public class AutoDateHistogramAggregationBuilder
         return new AutoDateHistogramAggregationBuilder(this, factoriesBuilder, metaData);
     }
 
-    @Override
-    protected void innerWriteTo(StreamOutput out) throws IOException {
-        out.writeVInt(numBuckets);
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
-            out.writeOptionalString(minimumIntervalExpression);
-        }
-    }
-
     @Override
     public String getType() {
         return NAME;
     }
 
+    public String getMinimumIntervalExpression() {
+        return minimumIntervalExpression;
+    }
+
+    public AutoDateHistogramAggregationBuilder setMinimumIntervalExpression(String minimumIntervalExpression) {
+        if (minimumIntervalExpression != null && !ALLOWED_INTERVALS.containsValue(minimumIntervalExpression)) {
+            throw new IllegalArgumentException(MINIMUM_INTERVAL_FIELD.getPreferredName() +
+                " must be one of [" + ALLOWED_INTERVALS.values().toString() + "]");
+        }
+        this.minimumIntervalExpression = minimumIntervalExpression;
+        return this;
+    }
+
     public AutoDateHistogramAggregationBuilder setNumBuckets(int numBuckets) {
         if (numBuckets <= 0) {
             throw new IllegalArgumentException(NUM_BUCKETS_FIELD.getPreferredName() + " must be greater than 0 for [" + name + "]");