Document requirement for cookie path when using paths other than /login

#### Context

* *node version*: 14.15.4
* *module version*: 11.0.2

#### What are you trying to achieve or the steps to reproduce ?
We wasted several hours trying to configure our login page to be something other than `/login`, in the example below we tried using `/foo.login`. After asking in the Hapi slack channel, it was pointed out to us that if you do not assign the cookie a path, it defaults to null and only works with the path `/login` and therefore breaks the code if you do not specify it as `/` for a different path. It would be appreciated if the documentation was updated with this an example or highlight that the path must be noted if you wish to using anything other than the default.

```const Hapi = require('@hapi/hapi')
const Bcrypt = require('bcrypt');

// create a server with a host and port
const server = new Hapi.Server({
host: 'localhost',
port: 3000
})

const users = [
{
username: 'john',
password: '$2a$10$iqJSHD.BGr0E2IxQwYgJmeP3NvhPrXAeLSaGCj6IR/XU5QtjVu5Tm', // 'secret'
name: 'John Doe',
id: '2133d32a'
}
];

async function start () {
await server.register(require('@hapi/cookie'));

server.auth.strategy('session', 'cookie', {
cookie: {
name: 'sid-example',
password: '!wsYhFA*C2U6nz=Bu^%A@^F#SF3&kSR6',
isSecure: false,
path: '/'
},
redirectTo: '/foo/login',
validateFunc: async (request, session) => {

const account = await users.find(
(user) => (user.id === session.id)
);

if (!account) {

return { valid: false };
}

return { valid: true, credentials: account };
}
});

server.auth.default('session');

server.route([
{
method: 'GET',
path: '/',
handler: function (request, h) {

return 'Welcome to the restricted home page!';
}
},
{
method: 'GET',
path: '/foo/login',
handler: function (request, h) {

return `

Login page

Please Log In

Username:

Password:



`;
},
options: {
auth: false
}
},
{
method: 'POST',
path: '/foo/login',
handler: async (request, h) => {

const { username, password } = request.payload;
const account = users.find(
(user) => user.username === username
);

if (!account || !(await Bcrypt.compare(password, account.password))) {

return h.view('/foo/login');
}

request.cookieAuth.set({ id: account.id });

return h.redirect('/');
},
options: {
auth: {
mode: 'try'
}
}
}
]);

// start your server
try {
await server.start()
} catch (err) {
console.error(err)
process.exit(1)
}

console.log('Server running at: ', server.info.uri)
}

start()
```