[ML] fixing datafeed bwc tests (#52908)

Re-enables bwc tests and fixes up code after backport of #52793

Author: benwtrent

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java

@@ -236,7 +236,7 @@ public DatafeedConfig(StreamInput in) throws IOException {
         } else {
             maxEmptySearches = null;
         }
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_7_0)) {
             indicesOptions = IndicesOptions.readIndicesOptions(in);
         } else {
             indicesOptions = SearchRequest.DEFAULT_INDICES_OPTIONS;
@@ -448,7 +448,7 @@ public void writeTo(StreamOutput out) throws IOException {
         if (out.getVersion().onOrAfter(Version.V_7_5_0)) {
             out.writeOptionalVInt(maxEmptySearches);
         }
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_7_0)) {
             indicesOptions.writeIndicesOptions(out);
         }
     }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedUpdate.java

@@ -156,7 +156,7 @@ public DatafeedUpdate(StreamInput in) throws IOException {
         } else {
             maxEmptySearches = null;
         }
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_7_0)) {
             indicesOptions = in.readBoolean() ? IndicesOptions.readIndicesOptions(in) : null;
         } else {
             indicesOptions = null;
@@ -207,7 +207,7 @@ public void writeTo(StreamOutput out) throws IOException {
         if (out.getVersion().onOrAfter(Version.V_7_5_0)) {
             out.writeOptionalInt(maxEmptySearches);
         }
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_7_0)) {
             if (indicesOptions != null) {
                 out.writeBoolean(true);
                 indicesOptions.writeIndicesOptions(out);

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/mixed_cluster/40_ml_datafeed_crud.yml

@@ -1,13 +1,5 @@
-setup:
-  - skip:
-      reason: "Waiting for backport of https://github.com/elastic/elasticsearch/pull/52793"
-      version: all
-
 ---
 "Test old cluster datafeed without aggs":
-  - skip:
-      version: "all"
-      reason: "Awaits fix: https://github.com/elastic/elasticsearch/issues/52739"
   - do:
       ml.get_datafeeds:
         datafeed_id: old-cluster-datafeed-without-aggs

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/40_ml_datafeed_crud.yml

@@ -1,7 +1,3 @@
-setup:
-  - skip:
-      reason: "Waiting for backport of https://github.com/elastic/elasticsearch/pull/52793"
-      version: all
 ---
 "Put job and datafeed without aggs in old cluster":
 

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/40_ml_datafeed_crud.yml

@@ -1,7 +1,4 @@
 setup:
-  - skip:
-      reason: "Waiting for backport of https://github.com/elastic/elasticsearch/pull/52793"
-      version: all
   - do:
      cluster.health:
         wait_for_status: green