Add type annotations and import missing dependencies

Added type annotations to CustomMarkdocTags to ensure type safety. Also, included missing imports for Schema and block, improving the integrity of the file.

packages/cms/keystatic/src/custom-components.tsx

@@ -1,3 +1,5 @@
+import type { Schema } from '@markdoc/markdoc';
+
 /**
  * @name CustomMarkdocComponents
  * @description Custom components for Markdoc. Please define your custom components here.
@@ -24,9 +26,10 @@ export const CustomMarkdocComponents: Record<
  * export const CustomMarkdocTags = {
  *  youtube: {
  *     render: "Youtube",
+ *     selfClosing: true,
  *  }
  * }
  */
-export const CustomMarkdocTags = {
+export const CustomMarkdocTags: Record<string, Schema> = {
   // define your custom tags here
 };