Introduce SonarCloud integration and resolve assorted violations (#575)

documentation-support/src/main/java/tech/picnic/errorprone/documentation/ExtractorType.java

@@ -25,6 +25,7 @@ enum ExtractorType {
     return identifier;
   }
 
+  @SuppressWarnings("java:S1452" /* The extractor returns data of an unspecified type. */)
   Extractor<?> getExtractor() {
     return extractor;
   }

documentation-support/src/test/java/tech/picnic/errorprone/documentation/DocumentationGeneratorTaskListenerTest.java

@@ -67,10 +67,11 @@ final class DocumentationGeneratorTaskListenerTest {
 
   @Test
   void excessArguments(@TempDir Path outputDirectory) {
+    String actualOutputDirectory = outputDirectory.toAbsolutePath() + " extra-arg";
     assertThatThrownBy(
             () ->
                 Compilation.compileWithDocumentationGenerator(
-                    outputDirectory.toAbsolutePath() + " extra-arg", "A.java", "package pkg;"))
+                    actualOutputDirectory, "A.java", "package pkg;"))
         .isInstanceOf(IllegalArgumentException.class)
         .hasMessage("Precisely one path must be provided");
   }