Add PreferHTTPRoute and Gateway protocol detection support

[lexfrei]

Summary

Add support for PreferHTTPRoute field in ClientConfig to allow operator to communicate with Grafana instance via HTTPRoute instead of Service, similar to existing PreferIngress functionality.

Motivation

When using Gateway API HTTPRoutes, the operator currently communicates with Grafana through the Service. However, in some scenarios (similar to Ingress use cases), it would be beneficial to communicate through the HTTPRoute to:

• Validate that the HTTPRoute is correctly configured
• Test the full ingress path including Gateway rules and filters
• Ensure end-to-end connectivity works as expected

Proposed Implementation

1. Add PreferHTTPRoute Field

type ClientConfig struct {
    // ... existing fields ...
    PreferHTTPRoute *bool `json:"preferHTTPRoute,omitempty"`
}

2. Gateway Protocol Detection

Implement Gateway lookup to determine correct protocol (HTTP/HTTPS):

• Look up Gateway resource from HTTPRoute.Spec.ParentRefs
• Find matching Listener by SectionName
• Detect protocol from Listener.Protocol or Listener.TLS configuration
• Fallback to hostname from HTTPRoute.Spec.Hostnames

3. AdminURL Construction

Build admin URL using detected protocol and hostname for operator-to-Grafana communication.

Complexity Considerations

This feature requires:

• Additional RBAC permissions to read Gateway resources
• Complex logic to match listeners and detect protocols
• Proper error handling for missing/incomplete Gateway information
• Comprehensive test coverage

Related

• Initial HTTPRoute support: feat(ingress): add HTTPRoute support for Grafana instances #2283 (removed this functionality to keep PR focused)
• Similar functionality exists for Ingress: PreferIngress field

Questions for Discussion

1. Is this functionality needed for HTTPRoute support, or is Service-based communication sufficient?
2. Should we support fallback scenarios (e.g., Gateway not found)?
3. What should be the behavior when multiple parentRefs are defined?
4. Should we also support extracting hostname from Gateway status if not specified in HTTPRoute?

[theSuess]

Just writing down my thoughts:

• We could instead name the field PreferExternalEndpoint which would deprecate the PreferIngress field
• This would also remove the confusion of PreferIngress also applying to openshift routes

Alternatively: We get rid of this field entirely and instruct people to use spec.external instead