fix: Add maven enforcer rule for JDK version, as 12+ fails

Before:
```
[ERROR] Tests run: 8, Failures: 0, Errors: 3, Skipped: 0, Time elapsed: 0.040 s <<< FAILURE! -- in cz.habarta.typescript.generator.NamingTest
[ERROR] cz.habarta.typescript.generator.NamingTest.testCombinations -- Time elapsed: 0.032 s <<< ERROR!
java.lang.NoSuchMethodError: 'void sun.misc.Unsafe.ensureClassInitialized(java.lang.Class)'
        at com.oracle.truffle.api.library.LibraryFactory.ensureLibraryInitialized(LibraryFactory.java:384)
```

Now, if you are not running Java 11:
```
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.5.0:enforce (enforce-java-version) on project typescript-generator:
[ERROR] Rule 0: org.apache.maven.enforcer.rules.version.RequireJavaVersion failed with message:
[ERROR] Detected JDK version 23.0.1 (JAVA_HOME=/opt/homebrew/Cellar/openjdk/23.0.1/libexec/openjdk.jdk/Contents/Home) is not in the allowed range [11,12).
```

Fixing it by appending the correct `JAVA_HOME`:
```
➤ JAVA_HOME=(/usr/libexec/java_home --version 11) mvn clean install
...
[INFO] BUILD SUCCESS
...
```

Author: Nthalk

pom.xml

@@ -160,6 +160,30 @@
     <build>
 
         <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-enforcer-plugin</artifactId>
+                <version>3.5.0</version>
+                <executions>
+                    <execution>
+                        <id>enforce-java-version</id>
+                        <goals>
+                            <goal>enforce</goal>
+                        </goals>
+                        <phase>validate</phase>
+                    </execution>
+                </executions>
+                <configuration>
+                    <rules>
+                        <requireMavenVersion>
+                            <version>[3,4]</version>
+                        </requireMavenVersion>
+                        <requireJavaVersion>
+                            <version>[11,12)</version>
+                        </requireJavaVersion>
+                    </rules>
+                </configuration>
+            </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>