Limit supported annotations to @ConfigurationProperties and @Configuration

Previously, the configuration property annotation processor declared
that it supported all annotation types. This hurt performance and
prevented incremental builds with Gradle when compiling source code
containing source-retention annotations.

This commit updates its supported annotation types to be only
`@ConfigurationProperties` and `@Configuration`. The latter is declared
to allow binding third-party classes returned from a `@Bean` method.

Fixes gh-23580

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -68,6 +68,13 @@ import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
  */
 class ConfigurationMetadataAnnotationProcessorTests extends AbstractMetadataGenerationTests {
 
+	@Test
+	void supportedAnnotations() {
+		assertThat(new ConfigurationMetadataAnnotationProcessor().getSupportedAnnotationTypes())
+				.containsExactlyInAnyOrder("org.springframework.boot.context.properties.ConfigurationProperties",
+						"org.springframework.context.annotation.Configuration");
+	}
+
 	@Test
 	void notAnnotated() {
 		ConfigurationMetadata metadata = compile(NotAnnotated.class);