Datanode config separation (#15701)

* Different variants of security configuration (from file, from mongo, insecure).
Encryption/decryption pattern used in practice.

* Reverting temporary changes

* More precise certificate presence check

* Added unit tests for testHasCert() method

* Datanode and opensearch configuration refactored

* code cleanup

* code cleanup

* code cleanup

* Node preflight config service refactored

* restbaseurl moved to OpensearchConfiguration

---------

Co-authored-by: Lukasz Kaminski <lukasz.kaminski@graylog.com>

data-node/src/main/java/org/graylog/datanode/process/OpensearchConfiguration.java

@@ -17,6 +17,7 @@
 package org.graylog.datanode.process;
 
 import org.graylog.datanode.management.Environment;
+import org.graylog.shaded.opensearch2.org.apache.http.HttpHost;
 
 import java.nio.file.Path;
 import java.util.LinkedHashMap;
@@ -24,7 +25,6 @@ import java.util.List;
 import java.util.Map;
 
 public record OpensearchConfiguration(
-        String opensearchVersion,
         Path opensearchDir,
         Path opensearchConfigDir,
         int httpPort,
@@ -64,4 +64,9 @@ public record OpensearchConfiguration(
         env.put("OPENSEARCH_PATH_CONF", opensearchConfigDir.resolve("opensearch").toAbsolutePath().toString());
         return env;
     }
+
+    public HttpHost getRestBaseUrl() {
+        final boolean sslEnabled = Boolean.parseBoolean(asMap().getOrDefault("plugins.security.ssl.http.enabled", "false"));
+        return new HttpHost("localhost", httpPort(), sslEnabled ? "https" : "http");
+    }
 }