[management,proxy] Add agentgateway integration (#7274)

* [management] Add agentgateway provider catalog entry

Allow Agent Network providers to target an operator-supplied agentgateway proxy while stamping trusted NetBird identity headers.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [proxy] Allow trusted Agent Network identity headers

Permit only the built-in identity injector to replace the two reserved agentgateway attribution headers while keeping them blocked for every other middleware.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [management,proxy] Add multi-vendor gateway routing

Let one Agent Network route declare multiple parser surfaces while preserving the existing singular vendor wire field.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [management] Update router test for model policies

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [proxy] Cover reserved header policy

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [management] Add agentgateway model discovery

Use agentgateway's OpenAI-compatible models endpoint and omit wildcard patterns until NetBird can authorize and price them consistently.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

---------

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

management/internals/modules/agentnetwork/modeldiscovery/discovery.go

@@ -52,9 +52,8 @@ const (
 )
 
 // ErrNoDiscovery is returned for a catalog entry that declares no listing
-// endpoint. Gateways vary too much to have one, and the caller should fall
-// back to the catalog list plus free-text entry rather than treating this as
-// a failure.
+// endpoint. The caller should fall back to the catalog list plus free-text
+// entry rather than treating this as a failure.
 var ErrNoDiscovery = errors.New("provider has no model-discovery endpoint")
 
 // ErrInvalidRequest marks a discovery failure caused by the caller's own input
@@ -356,6 +355,9 @@ func decorate(entry catalog.Provider, ids []listedModel) []Model {
 		if listed.id == "" {
 			continue
 		}
+		if entry.Discovery.ExactModelsOnly && strings.Contains(listed.id, "*") {
+			continue
+		}
 		if _, dup := seen[listed.id]; dup {
 			continue
 		}