Add java level profiles (#893)

These will get used by IDEs (e.g. IDEA IntelliJ) to set the appropriate java level if it differs from the default java level defined in the pom file.

In practice, maven-hpi-plugin will generate and manage the files used as activation markers for these profiles, depending on the java level required by the jenkins version the plugin required.

pom.xml

@@ -1453,5 +1453,27 @@
         <yarn.lint.skip>true</yarn.lint.skip>
       </properties>
     </profile>
+    <profile>
+      <id>java-level-17</id>
+      <activation>
+        <file>
+          <exists>target/java-level/17</exists>
+        </file>
+      </activation>
+      <properties>
+        <maven.compiler.release>17</maven.compiler.release>
+      </properties>
+    </profile>
+    <profile>
+      <id>java-level-21</id>
+      <activation>
+        <file>
+          <exists>target/java-level/21</exists>
+        </file>
+      </activation>
+      <properties>
+        <maven.compiler.release>21</maven.compiler.release>
+      </properties>
+    </profile>
   </profiles>
 </project>