Prometheus: Implement Streaming JSON Parser (#48477)

use `prometheusStreamingJSONParser` feature toggle to enable

pkg/tsdb/prometheus/client/cache.go

@@ -0,0 +1,55 @@
+package client
+
+import (
+	"sort"
+	"strings"
+
+	lru "github.com/hashicorp/golang-lru"
+)
+
+type ProviderCache struct {
+	provider promClientProvider
+	cache    *lru.Cache
+}
+
+type promClientProvider interface {
+	GetClient(map[string]string) (*Client, error)
+}
+
+func NewProviderCache(p promClientProvider) (*ProviderCache, error) {
+	cache, err := lru.New(500)
+	if err != nil {
+		return nil, err
+	}
+
+	return &ProviderCache{
+		provider: p,
+		cache:    cache,
+	}, nil
+}
+
+func (c *ProviderCache) GetClient(headers map[string]string) (*Client, error) {
+	key := c.key(headers)
+	if client, ok := c.cache.Get(key); ok {
+		return client.(*Client), nil
+	}
+
+	client, err := c.provider.GetClient(headers)
+	if err != nil {
+		return nil, err
+	}
+
+	c.cache.Add(key, client)
+	return client, nil
+}
+
+func (c *ProviderCache) key(headers map[string]string) string {
+	vals := make([]string, len(headers))
+	var i int
+	for _, v := range headers {
+		vals[i] = v
+		i++
+	}
+	sort.Strings(vals)
+	return strings.Join(vals, "")
+}