Issue #1919210 by vijaycs85, rahuldolas123: Create configuration schemas for text module.

core/modules/text/config/schema/text.schema.yml

+# Schema for the configuration files of the text module.
+
+text.settings:
+  type: mapping
+  label: 'Text settings'
+  mapping:
+    default_summary_length:
+      type: integer
+      label: 'Default summary length'