Omit properties deprecated at error level from new appendix

Closes gh-47622

Author: wilkinsona

buildSrc/src/main/java/org/springframework/boot/build/context/properties/ConfigurationProperty.java

@@ -97,7 +97,7 @@ static ConfigurationProperty fromJsonProperties(Map<String, Object> property) {
 				Deprecation.fromJsonProperties(deprecation));
 	}
 
-	record Deprecation(String reason, String replacement, String since) {
+	record Deprecation(String reason, String replacement, String since, String level) {
 
 		static Deprecation fromJsonProperties(Map<String, Object> property) {
 			if (property == null) {
@@ -106,7 +106,8 @@ static Deprecation fromJsonProperties(Map<String, Object> property) {
 			String reason = (String) property.get("reason");
 			String replacement = (String) property.get("replacement");
 			String since = (String) property.get("since");
-			return new Deprecation(reason, replacement, since);
+			String level = (String) property.get("level");
+			return new Deprecation(reason, replacement, since, level);
 		}
 
 	}

buildSrc/src/main/java/org/springframework/boot/build/context/properties/Snippets.java

@@ -30,6 +30,8 @@
 
 import org.gradle.api.file.FileCollection;
 
+import org.springframework.boot.build.context.properties.ConfigurationProperty.Deprecation;
+
 /**
  * Configuration properties snippets.
  *
@@ -118,7 +120,12 @@ String findXref(String name) {
 	}
 
 	private boolean shouldAdd(ConfigurationProperty property) {
-		return (property == null || property.isDeprecated() == this.deprecated);
+		return (property == null || (property.isDeprecated() == this.deprecated && !deprecatedAtErrorLevel(property)));
+	}
+
+	private boolean deprecatedAtErrorLevel(ConfigurationProperty property) {
+		Deprecation deprecation = property.getDeprecation();
+		return deprecation != null && "error".equals(deprecation.level());
 	}
 
 	private Asciidoc getAsciidoc(Snippet snippet, Table table) {