Add support for match_only_text field type (#284)

Author: jsoriano

test/packages/good/data_stream/foo/fields/some_fields.yml

@@ -32,3 +32,6 @@
 - name: vehicle_type
   type: constant_keyword
   value: truck
+- name: error.message
+  description: Error message.
+  type: match_only_text

versions/1/changelog.yml

@@ -13,6 +13,9 @@
   - description: Fix validation of dimension fields inside objects
     type: bugfix
     link: https://github.com/elastic/package-spec/pull/279
+  - description: Add support for match_only_text field type
+    type: enhancement
+    link: https://github.com/elastic/package-spec/issues/284
 - version: 1.4.1
   changes:
   - description: ML model file name now matches the id of the model.

versions/1/data_stream/fields/fields.spec.yml

@@ -22,6 +22,7 @@ spec:
         - histogram
         - constant_keyword
         - text
+        - match_only_text
         - keyword
         - long
         - integer