Update pnpm from v7 to v8

That suppose to help with Dependabot security updates not updating lockfile.

frontend/packages/api/README.md

@@ -4,7 +4,7 @@ Implementation of API methods for Remark42
 
 ## Development
 
-- If you don't have `pnpm` installed run `npm i -g pnpm@7`
+- If you don't have `pnpm` installed run `npm i -g pnpm@8`
 - Install dependencies `pnpm i`
 - Run development mode with `pnpm run dev`
 - Build lib with `pnpm run build`

frontend/packages/api/package.json

@@ -29,7 +29,7 @@
     "type-check": "tsc --noEmit",
     "lint-staged:lint": "eslint --fix --ext .cjs,.mjs,.ts"
   },
-  "packageManager": "pnpm@7.33.7",
+  "packageManager": "pnpm@8.15.9",
   "devDependencies": {
     "@types/node": "^18.0.5",
     "@typescript-eslint/eslint-plugin": "^5.33.1",