Disable SLM history in docs tests (#118979) (#119813)

The SLM history data stream was causing issues in the docs tests because
its presence was flaky and could result in the inability to remove
its index template, which in turn resulted in failing tests.

docs/build.gradle

@@ -76,6 +76,11 @@ testClusters.matching { it.name == "yamlRestTest"}.configureEach {
   setting 'script.painless.regex.enabled', 'true'
   setting 'xpack.security.enabled', 'false'
   setting 'path.repo', "${buildDir}/cluster/shared/repo"
+
+  // disable the ILM and SLM history for doc tests to avoid potential lingering tasks that'd cause test flakiness
+  setting 'indices.lifecycle.history_index_enabled', 'false'
+  setting 'slm.history_index_enabled', 'false'
+
   Closure configFile = {
     extraConfigFile it, file("src/test/cluster/config/$it")
   }