feat(core): Replace client-oauth2 with an in-repo package (#6266)

Co-authored-by: Marcus <marcus@n8n.io>

packages/@n8n/client-oauth2/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "@n8n/client-oauth2",
+  "version": "0.1.0",
+  "scripts": {
+    "clean": "rimraf dist .turbo",
+    "dev": "pnpm watch",
+    "typecheck": "tsc",
+    "build": "tsc -p tsconfig.build.json",
+    "format": "prettier --write . --ignore-path ../../../.prettierignore",
+    "lint": "eslint --quiet .",
+    "lintfix": "eslint . --fix",
+    "watch": "tsc -p tsconfig.build.json --watch",
+    "test": "jest",
+    "test:dev": "jest --watch"
+  },
+  "main": "dist/index.js",
+  "module": "src/index.ts",
+  "types": "dist/index.d.ts",
+  "files": [
+    "dist/**/*"
+  ],
+  "dependencies": {
+    "axios": "^0.21.1"
+  }
+}