build(docs-infra): add a tool to create new examples (#39283)

This tool can be run from anywhere in the aio folder as:

```sh
yarn create-example <example-name>
```

It will create some basic scaffold files to get the example started.
After creation the developer should then use `yarn boilerplate:add`
or similar to ensure that the example can be run and tested.

You can optionally provide an absolute path to a pre-existing CLI
project and it will copy over appropriate files (ignoring boilerplate)
to the newly created example.

```sh
yarn create-example <example-name> /path/to/other/cli/project
```

Fixes #39275

PR Close #39283

aio/tools/examples/constants.js

@@ -0,0 +1,6 @@
+const path = require('canonical-path');
+
+exports.EXAMPLES_BASE_PATH = path.resolve(__dirname, '../../content/examples');
+exports.EXAMPLE_CONFIG_FILENAME = 'example-config.json';
+exports.SHARED_PATH = path.resolve(__dirname, 'shared');
+exports.STACKBLITZ_CONFIG_FILENAME = 'stackblitz.json';