Add schema.yml.

Closes #3528820

config/schema/views_scored_sort.schema.yml

+views_scored_sort.scoring_config:
+  type: mapping
+  label: 'Scoring configuration for views'
+  mapping:
+    views:
+      type: mapping
+      label: 'Views'
+      mapping:
+        '*':
+          type: mapping
+          label: 'Displays'
+          mapping:
+            '*':
+              type: mapping
+              label: 'Field scoring config'
+              mapping:
+                '*':
+                  type: mapping
+                  label: 'Field settings'
+                  mapping:
+                    score:
+                      type: float
+                      label: 'Score'
+                    direction:
+                      type: string
+                      label: 'Direction'
+                      required: false
+                    mode:
+                      type: string
+                      label: 'Scoring mode'
+                      required: false
+                    match_required:
+                      type: boolean
+                      label: 'Match Required'
+                      required: false
+                    months_decay:
+                      type: integer
+                      label: 'Months per decay'
+                      required: false
+                    type:
+                      type: string
+                      label: 'Field type'