[SPIKE] What functionality should be present in policies, filters, backendRef, and gateway class parameters?

[mpstefan]

Before implementing policies, we need to determine what logical groups of native NGINX functionality make sense to put together so that we limit breaking changes going forward and avoid creating groups that are too large or too small.

In this spike, we want to answer these specific questions:

1. Should create policies around granularity (GatewayClass, Gateway, Route), use cases (authentication, observability, etc), or something else?
2. Roughly how many policy types would be created if our set of NGINX directives were included in NGF with the above grouping?
3. What need is there, if any, to keep the current design for the data plane CRD?
4. What roles apply to each one of the groups?

[mpstefan]

Blocked by #1410