Adapt Gateway plugin reference into the AI Policy entity reference

## Overview

AI Policies are wrappers around Gateway plugins. The [Gateway reference page](https://developer.konghq.com/gateway/entities/plugin/#custom-plugins) contains a lot of crucial details that apply to AI Policies but are absent from the existing page. We might want to include missing details in the AI Policy reference page, or create a separate reference page for all missing details (TBD).

## DoD

Add information to the [policies](https://developer.konghq.com/ai-gateway/entities/ai-policy/) page to contain:

- [custom policies](https://konghq.aha.io/features/AI-107)
- policy priority (verify how they work not just migrate the page)
- [Conditional execution](https://developer.konghq.com/gateway/entities/plugin/#conditional-plugin-execution)
- [Cloning plugins](https://developer.konghq.com/gateway/entities/plugin/#cloning-plugins)
- [Protocols](https://developer.konghq.com/gateway/entities/plugin/#protocols)
----

We need to adapt the following sections of the Plugins reference:
- [Custom plugins](https://developer.konghq.com/gateway/entities/plugin/) - we are shipping AI GW support for it along with 2.1
- How do plugins work? - essentially, the mechanism is the same, we can double-check in case there are any slight differences
- [Scoping section and sub-sections](https://developer.konghq.com/gateway/entities/plugin/#scoping-plugins) - this will differ, you can get AI Policies scope by running:

```curl
curl --request GET \
--url https://us.api.konghq.com/v1/ai-gateways/$AI_GATEWAY_ID/available-policies \
--header 'Accept: application/json, application/problem+json' \
--header "Authorization: $KONNECT_TOKEN" \
--header 'Content-Type: application/json'
```
- [Plugin priority](https://developer.konghq.com/gateway/entities/plugin/#plugin-priority) - we might also want to add the priority to the infobox for AI Policies like we do for Plugins
- [Conditional execution](https://developer.konghq.com/gateway/entities/plugin/#conditional-plugin-execution)
- [Cloning plugins](https://developer.konghq.com/gateway/entities/plugin/#cloning-plugins)
- [Protocols](https://developer.konghq.com/gateway/entities/plugin/#protocols)

Size: M to L

Start with the existing AI Policy reference at developer.konghq.com/ai-gateway/entities/ai-policy/ and compare it with the Gateway plugin reference sections listed in the issue. Run the available-policies curl request to verify AI Policy scope and check how priority and execution details differ. Done means the policies page covers custom policies, scoping, priority, conditional execution, cloning, and protocols with verified AI Gateway behavior.

Written by the indexing model from the issue text.