This PR was submitted for the 4.4 branch but it was squashed and merged into the 5.1-dev branch instead (closes #31889).

Discussion
----------

[Lock] add mongodb store

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes (requires `ext-mongodb` and `mongodb/mongodb` to test)
| Fixed tickets | #27345
| License       | MIT
| Original Doc PR        | symfony/symfony-docs#9807
| Remove from 4.3 Doc PR | symfony/symfony-docs#11686
| Add to 4.4 Doc PR | symfony/symfony-docs#11735

Looks like I messed up `kralos:27345-lock-mongodb` with a force push (trying to fix ci issues) right before it was merged to `master` (`4.3.0`).

see #27648

**Description**
We should support Semaphore Locks with a MongoDB back end to allow those that already use MongoDB as a distributed storage engine.

Symfony already partially supports MongoDB for session storage: `Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler`

**Example**

```php
$client = new MongoDb\Client();

$store = new Symfony\Component\Lock\Store\MongoDbStore(
    $client
    array(
        'database' => 'my-app',
    )
);
$lockFactory = new Symfony\Component\Lock\Factory($store);
$lock = $lockFactory->createLock('my-resource');
```

Commits
-------

a6bfa59 [Lock] add mongodb store