Add text/markdown MediaType constant

Issue: SPR-14192

Author: venilnoronha

spring-web/src/main/java/org/springframework/http/MediaType.java

@@ -191,6 +191,16 @@ public class MediaType extends MimeType implements Serializable {
 	 */
 	public final static String TEXT_HTML_VALUE = "text/html";
 
+	/**
+	 * Public constant media type for {@code text/markdown}.
+	 */
+	public final static MediaType TEXT_MARKDOWN;
+
+	/**
+	 * A String equivalent of {@link MediaType#TEXT_MARKDOWN}.
+	 */
+	public final static String TEXT_MARKDOWN_VALUE = "text/markdown";
+
 	/**
 	 * Public constant media type for {@code text/plain}.
 	 *  */
@@ -230,6 +240,7 @@ public class MediaType extends MimeType implements Serializable {
 		IMAGE_PNG = valueOf(IMAGE_PNG_VALUE);
 		MULTIPART_FORM_DATA = valueOf(MULTIPART_FORM_DATA_VALUE);
 		TEXT_HTML = valueOf(TEXT_HTML_VALUE);
+		TEXT_MARKDOWN = valueOf(TEXT_MARKDOWN_VALUE);
 		TEXT_PLAIN = valueOf(TEXT_PLAIN_VALUE);
 		TEXT_XML = valueOf(TEXT_XML_VALUE);
 	}