[HttpFoundation] MongoDbSessionHandler supports auto expiry and auto index creation

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11508
| License       | MIT
| Doc PR        | no

ToDo

 * [x] Fix Tests

Looking for feedback on this early PR.


This adds a config option that disables the PHP GC method call from doing anything,
It also means that the write method sets up the auto expiring index.


Ref: #11508
Rather than most of the existing method body in an `if` statement, it would be preferable to simply do the following at the top of the function:

```
if (false !== $this->options['expiry_field']) {
    return true;
}
```

That keeps the diff smaller, which benefits anyone working on the file in the future.