fix: update delegateMock used in ENT (#18149)

### Description

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The mock is used in `http_ent_test` file which caused lint failures. For
OSS->ENT parity adding the same change here.

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Identified in OSS->ENT [merge
PR](https://github.com/hashicorp/consul-enterprise/pull/6328)

### PR Checklist

* [ ] ~updated test coverage~
* [ ] ~external facing docs updated~
* [x] appropriate backport labels added
* [ ] ~not a security concern~

agent/delegate_mock_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/hashicorp/consul/agent/consul"
 	"github.com/hashicorp/consul/agent/structs"
 	"github.com/hashicorp/consul/lib"
+	"github.com/hashicorp/consul/proto-public/pbresource"
 )
 
 type delegateMock struct {
@@ -76,3 +77,7 @@ func (m *delegateMock) Stats() map[string]map[string]string {
 func (m *delegateMock) ReloadConfig(config consul.ReloadableConfig) error {
 	return m.Called(config).Error(0)
 }
+
+func (m *delegateMock) ResourceServiceClient() pbresource.ResourceServiceClient {
+	return nil
+}