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

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

packages/@n8n/client-oauth2/tsconfig.build.json

@@ -0,0 +1,12 @@
+{
+	"extends": "./tsconfig.json",
+	"compilerOptions": {
+		"rootDir": "src",
+		"outDir": "dist",
+		"types": ["node"],
+		"noEmit": false,
+		"tsBuildInfoFile": "dist/build.tsbuildinfo"
+	},
+	"include": ["src/**/*.ts"],
+	"exclude": ["test/**"]
+}