[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
> But only for records that have not had activity, as they will have the new expireAt set based on whatever the maxlifetime may have been changed to.

Good point! I missed that in my initial comment. No objection then, provided Symfony is OK with reading the `session.gc_maxlifetime` INI value here (I'm still curious what @Tobion was referring to).