Plugins: Refactor cleaning of call resource response headers (#67145)

First part of #66889 moving cleaning of call resource response headers 
within plugin management client.

pkg/services/pluginsintegration/clientmiddleware/resource_response_middleware.go

@@ -0,0 +1,65 @@
+package clientmiddleware
+
+import (
+	"context"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/util/proxyutil"
+)
+
+// NewResourceResponseMiddleware creates a new plugins.ClientMiddleware
+// that will enforce HTTP header rules for backend.CallResourceResponse's.
+func NewResourceResponseMiddleware() plugins.ClientMiddleware {
+	return plugins.ClientMiddlewareFunc(func(next plugins.Client) plugins.Client {
+		return &ResourceResponseMiddleware{
+			next: next,
+		}
+	})
+}
+
+type ResourceResponseMiddleware struct {
+	next plugins.Client
+}
+
+func (m *ResourceResponseMiddleware) QueryData(ctx context.Context, req *backend.QueryDataRequest) (*backend.QueryDataResponse, error) {
+	return m.next.QueryData(ctx, req)
+}
+
+func (m *ResourceResponseMiddleware) CallResource(ctx context.Context, req *backend.CallResourceRequest, sender backend.CallResourceResponseSender) error {
+	if req == nil || sender == nil {
+		return m.next.CallResource(ctx, req, sender)
+	}
+
+	processedStreams := 0
+	wrappedSender := callResourceResponseSenderFunc(func(res *backend.CallResourceResponse) error {
+		if processedStreams == 0 {
+			proxyutil.SetProxyResponseHeaders(res.Headers)
+		}
+
+		processedStreams++
+		return sender.Send(res)
+	})
+
+	return m.next.CallResource(ctx, req, wrappedSender)
+}
+
+func (m *ResourceResponseMiddleware) CheckHealth(ctx context.Context, req *backend.CheckHealthRequest) (*backend.CheckHealthResult, error) {
+	return m.next.CheckHealth(ctx, req)
+}
+
+func (m *ResourceResponseMiddleware) CollectMetrics(ctx context.Context, req *backend.CollectMetricsRequest) (*backend.CollectMetricsResult, error) {
+	return m.next.CollectMetrics(ctx, req)
+}
+
+func (m *ResourceResponseMiddleware) SubscribeStream(ctx context.Context, req *backend.SubscribeStreamRequest) (*backend.SubscribeStreamResponse, error) {
+	return m.next.SubscribeStream(ctx, req)
+}
+
+func (m *ResourceResponseMiddleware) PublishStream(ctx context.Context, req *backend.PublishStreamRequest) (*backend.PublishStreamResponse, error) {
+	return m.next.PublishStream(ctx, req)
+}
+
+func (m *ResourceResponseMiddleware) RunStream(ctx context.Context, req *backend.RunStreamRequest, sender *backend.StreamSender) error {
+	return m.next.RunStream(ctx, req, sender)
+}