Add detailed_metrics support to global ratelimit config

https://github.com/envoyproxy/ratelimit/issues/461 added support for dynamic [`detailed_metrics`](https://github.com/envoyproxy/ratelimit#including-detailed-metrics-for-unspecified-values) to the ratelimit service.

All the API dependencies are already present, [I did a quick test](https://github.com/crinjes/gateway/commit/35a3be9fba6733e3969fe719ed185818bb85054c) and believe the only thing required to enable the use in gateway is to add a boolean flag very similar to `shadowMode` to the `BackendTrafficPolicy` configuration.

This would allow something like:

```yaml
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: BackendTrafficPolicy
spec:
rateLimit:
global:
rules:
- clientSelectors:
- headers:
- name: x-client-id
type: Distinct
detailedMetric: true # <<<
limit:
requests: 10
unit: Minute
shared: true
```

For example, if there were one request with header `x-client-id: 1234` and four requests with `x-client-id: 4567`, the ratelimit service currentls would show the metrics like this:

```
ratelimit_service_rate_limit_total_hits{domain="...",key1="...",key2="rule-0-match-0"} 5
```

By enabling `detailed_metrics`, the resulting metrics would look like this:
```
ratelimit_service_rate_limit_total_hits{domain="...",key1="...",key2="rule-0-match-0_1234"} 1
ratelimit_service_rate_limit_total_hits{domain="...",key1="...",key2="rule-0-match-0_4567"} 4
```

This makes the `ratelimit_service_rate_limit_near_limit` and `ratelimit_service_rate_limit_over_limit` more useful, at the potential cost of very high metrics cardinality if not used carefully.