feat: add setMeta command

packages/core/src/commands/setMeta.ts

@@ -0,0 +1,18 @@
+import { Command, RawCommands } from '../types'
+
+declare module '@tiptap/core' {
+  interface Commands {
+    setMeta: {
+      /**
+       * Store a metadata property in the current transaction.
+       */
+      setMeta: (key: string, value: any) => Command,
+    }
+  }
+}
+
+export const setMeta: RawCommands['setMeta'] = (key, value) => ({ tr }) => {
+  tr.setMeta(key, value)
+
+  return true
+}