Added JSON schema for mkdocs-awesome-nav plugin (#8341)

* Add JSON schema for external plugin - "mkdocs-awesome-nav".

* Add reference to 'awesome-nav' plugin in external plugins schema.

* art: Fix missing newline at end of file in plugins schema files.

docs/schema/plugins.json

@@ -63,6 +63,9 @@
     "external": {
       "description": "External plugins, schema provided by us",
       "anyOf": [
+        {
+          "$ref": "plugins/external/awesome-nav.json"
+        },
         {
           "$ref": "plugins/external/gen-files.json"
         },

docs/schema/plugins/external/awesome-nav.json

@@ -0,0 +1,29 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema",
+  "title": "Custom advanced navigation config for MkDocs using extra YAML files.",
+  "oneOf": [
+    {
+      "markdownDescription": "https://github.com/lukasgeiter/mkdocs-awesome-nav",
+      "const": "awesome-nav"
+    },
+    {
+      "type": "object",
+      "properties": {
+        "awesome-nav": {
+          "type": "object",
+          "markdownDescription": "https://lukasgeiter.github.io/mkdocs-awesome-nav",
+          "properties": {
+            "filename": {
+              "title": "The YAML file that defines the navigation",
+              "markdownDescription": "https://lukasgeiter.github.io/mkdocs-awesome-nav",
+              "type": "string",
+              "default": ".nav.yml"
+            }
+          },
+          "additionalProperties": false
+        }
+      },
+      "additionalProperties": false
+    }
+  ]
+}