Experimental feature flags and processes

### Code of Conduct

- [x] I agree to follow Django's Code of Conduct

### Feature Description

Introduce official "Feature Flag" mechanism in Django. This can be done either by taking inspiration from https://waffle.readthedocs.io/en/stable/ and https://cfpb.github.io/django-flags/ or maybe by looking into including these into cores.

[TBD] A detailed process on how to handle API stability (or not) of features behind a flag

### Problem

The current development process of Django is slow. This is in part due to our commitment to backwards compatibility.
This means it is hard to test a new feature API directly in django/django because if we get it wrong we can't easily change it.
An experimental feature flag would help us overcome this, possibly making Django development faster

### Request or proposal

proposal

### Additional Details

[edit] Adding the link to the previously existing DEP as per @LilyFoote 's comment:
[DEP 2 - experimental APIs](https://github.com/django/deps/blob/main/draft/0002-experimental-apis.rst)

### Implementation Suggestions

_No response_