Add spring-security.xsd symlink

Closes gh-13131

config/src/main/resources/org/springframework/security/config/spring-security.xsd

@@ -0,0 +1 @@
+spring-security-5.7.xsd

config/src/test/java/org/springframework/security/config/doc/XsdDocumentedTests.java

@@ -150,8 +150,8 @@ public class XsdDocumentedTests {
 				.getParentFile()
 				.list((dir, name) -> name.endsWith(".xsd"));
 		// @formatter:on
-		assertThat(schemas.length).isEqualTo(19)
-				.withFailMessage("the count is equal to 19, if not then schemaDocument needs updating");
+		assertThat(schemas.length).isEqualTo(20)
+				.withFailMessage("the count is equal to 20, if not then schemaDocument needs updating");
 	}
 
 	/**