Update developer guide (#4128)

Signed-off-by: Tomoyuki Morita <moritato@amazon.com>

Author: ykmr1224

DEVELOPER_GUIDE.rst

@@ -17,15 +17,15 @@ Prerequisites
 JDK
 ---
 
-OpenSearch builds using Java 11 at a minimum and supports JDK 11, 14 and 17. This means you must have a JDK of supported version installed with the environment variable `JAVA_HOME` referencing the path to Java home for your JDK installation::
+OpenSearch SQL plugin requires Java 21 for development and runtime. This means you must have JDK 21 installed with the environment variable `JAVA_HOME` referencing the path to Java home for your JDK installation::
 
    $ echo $JAVA_HOME
-   /Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home
+   /Library/Java/JavaVirtualMachines/jdk-21.jdk/Contents/Home
 
    $ java -version
-    openjdk version "11.0.1" 2018-10-16
-    OpenJDK Runtime Environment 18.9 (build 11.0.1+13)
-    OpenJDK 64-Bit Server VM 18.9 (build 11.0.1+13, mixed mode)
+   openjdk version "21.0.8" 2024-07-16 LTS
+   OpenJDK Runtime Environment (build 21.0.8+13-LTS)
+   OpenJDK 64-Bit Server VM (build 21.0.8+13-LTS, mixed mode, sharing)
 
 Here are the official instructions on how to set ``JAVA_HOME`` for different platforms: https://docs.oracle.com/cd/E19182-01/820-7851/inst_cli_jdk_javahome_t/. 
 
@@ -78,12 +78,12 @@ You can develop the plugin in your favorite IDEs such as Eclipse and IntelliJ ID
 Java Language Level
 -------------------
 
-Although later version of JDK is required to build the plugin, the Java language level needs to be Java 8 for compatibility. Only in this case your plugin works with OpenSearch running against JDK 8. Otherwise it will raise runtime exception when executing new API from new JDK. In case your IDE doesn’t set it right, you may want to double check your project setting after import.
+The plugin requires Java 21 for both development and runtime. Make sure your IDE is configured to use Java 21 as the project SDK and language level. In case your IDE doesn't set it right, you may want to double check your project setting after import.
 
 Remote Debugging
 ----------------
 
-Firstly you need to add the following configuration to the JVM used by your IDE. For Intellij IDEA, it should be added to ``<OpenSearch installation>/config/jvm.options`` file. After configuring this, an agent in JVM will listen on the port when your OpenSearch bootstraps and wait for IDE debugger to connect. So you should be able to debug by setting up a “Remote Run/Debug Configuration”::
+Firstly you need to add the following configuration to the JVM used by your IDE. For Intellij IDEA, it should be added to ``<OpenSearch installation>/config/jvm.options`` file. After configuring this, an agent in JVM will listen on the port when your OpenSearch bootstraps and wait for IDE debugger to connect. So you should be able to debug by setting up a "Remote Run/Debug Configuration"::
 
    -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005
 
@@ -94,7 +94,7 @@ running.
 
    ./gradlew opensearch-sql:run -DdebugJVM
 
-To connect to the cluster with the debugger in an IDE, you’ll need to
+To connect to the cluster with the debugger in an IDE, you'll need to
 connect to that port. For IntelliJ, see `attaching to a remote process <https://www.jetbrains.com/help/idea/attach-to-process.html#attach-to-remote>`_.
 
 License Header
@@ -138,10 +138,10 @@ The plugin codebase is in standard layout of Gradle project::
    ├── build.gradle
    ├── config
    ├── docs
-   │   ├── attributions.md
-   │   ├── category.json
-   │   ├── dev
-   │   └── user
+   │   ├── attributions.md
+   │   ├── category.json
+   │   ├── dev
+   │   └── user
    ├── gradle.properties
    ├── gradlew
    ├── gradlew.bat
@@ -273,7 +273,7 @@ Building and Running Tests
 Gradle Build
 ------------
 
-Most of the time you just need to run ./gradlew build which will make sure you pass all checks and testing. While you’re developing, you may want to run specific Gradle task only. In this case, you can run ./gradlew with task name which only triggers the task along with those it depends on. Here is a list for common tasks:
+Most of the time you just need to run ./gradlew build which will make sure you pass all checks and testing. While you're developing, you may want to run specific Gradle task only. In this case, you can run ./gradlew with task name which only triggers the task along with those it depends on. Here is a list for common tasks:
 
 .. list-table::
    :widths: 30 50
@@ -304,7 +304,7 @@ Most of the time you just need to run ./gradlew build which will make sure you p
    * - ./gradlew spotlessApply
      - Automatically apply spotless code style changes.
 
-For integration test, you can use ``-Dtests.class`` “UT full path” to run a task individually. For example ``./gradlew :integ-test:integTest -Dtests.class="*QueryIT"``.
+For integration test, you can use ``-Dtests.class`` "UT full path" to run a task individually. For example ``./gradlew :integ-test:integTest -Dtests.class="*QueryIT"``.
 
 To run the task above for specific module, you can do ``./gradlew :<module_name>:task``. For example, only build core module by ``./gradlew :core:build``.