docs(examples): Add NestJS example (#688)

Uses Node.js SDK
Uses a Nest Guard with external default Arcjet configuration file Allows each controller to augment the Arcjet configuration

examples/nodejs-nestjs/.env.local.example

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+ARCJET_KEY=

examples/nodejs-nestjs/.eslintrc.js

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+module.exports = {
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    project: 'tsconfig.json',
+    tsconfigRootDir: __dirname,
+    sourceType: 'module',
+  },
+  plugins: ['@typescript-eslint/eslint-plugin'],
+  extends: [
+    'plugin:@typescript-eslint/recommended',
+    'plugin:prettier/recommended',
+  ],
+  root: true,
+  env: {
+    node: true,
+    jest: true,
+  },
+  ignorePatterns: ['.eslintrc.js'],
+  rules: {
+    '@typescript-eslint/interface-name-prefix': 'off',
+    '@typescript-eslint/explicit-function-return-type': 'off',
+    '@typescript-eslint/explicit-module-boundary-types': 'off',
+    '@typescript-eslint/no-explicit-any': 'off',
+  },
+};

examples/nodejs-nestjs/.gitignore

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+# compiled output
+/dist
+/node_modules
+/build
+
+# Logs
+logs
+*.log
+npm-debug.log*
+pnpm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# OS
+.DS_Store
+
+# Tests
+/coverage
+/.nyc_output
+
+# IDEs and editors
+/.idea
+.project
+.classpath
+.c9/
+*.launch
+.settings/
+*.sublime-workspace
+
+# IDE - VSCode
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+
+# dotenv environment variable files
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# temp directory
+.temp
+.tmp
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json

examples/nodejs-nestjs/.prettierrc

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+{
+  "singleQuote": true,
+  "trailingComma": "all"
+}

examples/nodejs-nestjs/README.md

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+<a href="https://arcjet.com" target="_arcjet-home">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="https://arcjet.com/arcjet-logo-minimal-dark-mark-all.svg">
+    <img src="https://arcjet.com/arcjet-logo-minimal-light-mark-all.svg" alt="Arcjet Logo" height="128" width="auto">
+  </picture>
+</a>
+
+# Arcjet Protection with NestJS for Node.js
+
+This example shows how to use Arcjet to protect [NestJS](https://nestjs.com/) apps using the Node.js SDK.
+
+## How to use
+
+1. From the root of the project, install the SDK dependencies.
+
+   ```bash
+   npm ci
+   ```
+
+2. Enter this directory and install the example's dependencies.
+
+   ```bash
+   cd examples/nodejs-nestjs
+   npm ci
+   ```
+
+3. Rename `.env.example` to `.env` and add your Arcjet key.
+
+4. Start the server.
+
+   ```bash
+   npm start
+   ```
+
+5. Visit `http://localhost:3000/` in a browser.
+
+6. Visit `http://localhost:3000/protected` in a browser and refresh the page to trigger the rate limit.
+
+7. Test shield by making this request 5 or more times:
+
+    ```bash
+    curl -v -H "x-arcjet-suspicious: true" http://localhost:3000
+    ```
+
+## How it works
+
+[ArcjetGuard](src/arcjet/arcjet.guard.ts) is a NestJS Guard, which is a type of middleware that is used to determine whether a request should be handled by the route handler or not. Guards have a single responsibility. They determine whether a request will be handled by the route handler, depending on certain conditions like permissions or roles.
+
+ArcjetGuard is defined as a provider in one or more modules, such as [AppModule](src/app.module.ts) and [ProtectedModule](src/protected/protected.module.ts). At this point, it's also possible to augment the rules from the default values by prefixing the ArcjetGuard provider definition with an extra, inline provider definition, as shown here. Check the [Node.js SDK Configuration documentation](https://docs.arcjet.com/reference/nodejs#configuration) for information on the rules available.
+
+```json
+providers: [
+   ProtectedService,
+   {
+      provide: 'ARCJET_RULES',
+      useValue: [
+         fixedWindow({
+            mode: "LIVE",
+            window: "1m",
+            max: 1,
+         }),
+      ],
+   },
+   ArcjetGuard,
+]
+```
+
+Finally, ArcjetGuard is defined in controllers with the following line:
+
+```js
+...
+
+@Controller()
+@UseGuards(ArcjetGuard)
+export class AppController {
+   ...
+```

examples/nodejs-nestjs/nest-cli.json

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+{
+  "$schema": "https://json.schemastore.org/nest-cli",
+  "collection": "@nestjs/schematics",
+  "sourceRoot": "src",
+  "compilerOptions": {
+    "deleteOutDir": true
+  }
+}