Adjust ILM policy version and re-enable BWC testing

This re-enables the BWC removed in elastic#73625 now that elastic#73624 has been merged

build.gradle

@@ -170,9 +170,9 @@ tasks.register("verifyVersions") {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
+boolean bwc_tests_enabled = true
 // place a PR link here when committing bwc changes:
-String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/73624"
+String bwc_tests_disabled_issue = ""
 /*
  * FIPS 140-2 behavior was fixed in 7.11.0. Before that there is no way to run elasticsearch in a
  * JVM that is properly configured to be in fips mode with BCFIPS. For now we need to disable

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/LifecyclePolicy.java

@@ -99,7 +99,7 @@ public LifecyclePolicy(StreamInput in) throws IOException {
         type = in.readNamedWriteable(LifecycleType.class);
         name = in.readString();
         phases = Collections.unmodifiableMap(in.readMap(StreamInput::readString, Phase::new));
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_14_0)) {
             this.metadata = in.readMap();
         } else {
             this.metadata = null;
@@ -134,7 +134,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeNamedWriteable(type);
         out.writeString(name);
         out.writeMap(phases, StreamOutput::writeString, (o, val) -> val.writeTo(o));
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_14_0)) {
             out.writeMap(this.metadata);
         }
     }