#23 Start to add schema for static sources in pp yamls

FRE/fre_pp.json

@@ -252,6 +252,38 @@
                 },
                 "minItems": 1,
                 "uniqueItems": true
+              },
+              "static": {
+                "type": "array",
+                "items": {
+                  "type": "object",
+                  "properties": {
+                    "sources": {
+                      "description": "History files to include this static source",
+                      "type": "array",
+                      "items": {
+                        "type": "string"
+                      }
+                    },
+                    "freq": {
+                      "description": "Static sources should have a frequency of P0[M/Y]",
+                      "type": "string"
+                    },
+                    "variables": {
+                      "description": "Variables for the static source",
+                      "type": "array",
+                      "items": {
+                        "type": "string"
+                      }
+                    },
+                    "history_file": {
+                      "description": "Path to history file if static source is for offline diagnostics (if history file not included in main history_dir",
+                      "type": "string"
+                    }
+                  },
+                  "required": ["sources"],
+                  "additional_properties": false
+                }
               }
             },
             "required": [