Improves disabled fielddata error message (#23841)

Closes #22768

core/src/main/java/org/elasticsearch/index/mapper/TextFieldMapper.java

@@ -287,7 +287,7 @@ public class TextFieldMapper extends FieldMapper {
             if (fielddata == false) {
                 throw new IllegalArgumentException("Fielddata is disabled on text fields by default. Set fielddata=true on [" + name()
                         + "] in order to load fielddata in memory by uninverting the inverted index. Note that this can however "
-                        + "use significant memory.");
+                                + "use significant memory. Alternatively use a keyword field instead.");
             }
             return new PagedBytesIndexFieldData.Builder(fielddataMinFrequency, fielddataMaxFrequency, fielddataMinSegmentSize);
         }