Issue #1919164 by Vikas Negi, sandipmkhairnar, vijaycs85: Create configuration...

Issue #1919164 by Vikas Negi, sandipmkhairnar, vijaycs85: Create configuration schemas for field module.

core/modules/field/config/schema/field.schema.yml

+# Schema for configuration files of the Field module.
+
+field.settings:
+  type: mapping
+  label: 'Field settings'
+  mapping:
+    purge_batch_size:
+      type: integer
+      label: 'Maximum number of field data records to purge'