fix: add slf4j-simple dependency to engine-agent

This dependency had been changed to slf4j-api to prevent bothering users with an implementation of slf4j. However, the engine-agent is not supposed to be included as a dependency by users. It's sole purpose is running the engine in a testcontainer. Doing this requires an implementation of slf4j.

engine-agent/pom.xml

@@ -34,6 +34,14 @@
       <artifactId>slf4j-api</artifactId>
     </dependency>
 
+    <!--  Usually we don't want to provide an slf4j implementation in this project. This modules
+      is the only exception to this rule. This is because we need to provide the engine with an
+      implementation, and since this runs in a docker container the user won't be providing it. -->
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-simple</artifactId>
+    </dependency>
+
     <dependency>
       <groupId>io.grpc</groupId>
       <artifactId>grpc-stub</artifactId>
@@ -80,6 +88,21 @@
           </execution>
         </executions>
       </plugin>
+
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-dependency-plugin</artifactId>
+        <configuration>
+          <failOnWarning>true</failOnWarning>
+          <ignoredUnusedDeclaredDependencies>
+            <!-- Required to provide the engine with a slf4j implementation. Usually we should
+                only add an actual slf4j implementation in the test scope. However, since this
+                module will run the engine in a docker container we need to provide the actual
+                implementation here. -->
+            <ignoredUnusedDeclaredDependency>org.slf4j:slf4j-simple</ignoredUnusedDeclaredDependency>
+          </ignoredUnusedDeclaredDependencies>
+        </configuration>
+      </plugin>
     </plugins>
   </build>
 </project>