Add SendWithContext method to Kibana client. (elastic#16515) (elastic…

…#16542)

This allows passing in context for http requests made to Kibana.
Requirement for elastic/apm-server#3185

libbeat/kibana/client.go

@@ -19,6 +19,7 @@ package kibana
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -181,9 +182,16 @@ func (conn *Connection) Request(method, extraPath string,
 func (conn *Connection) Send(method, extraPath string,
 	params url.Values, headers http.Header, body io.Reader) (*http.Response, error) {
 
+	return conn.SendWithContext(context.Background(), method, extraPath, params, headers, body)
+}
+
+// SendWithContext sends an application/json request to Kibana with appropriate kbn headers and the given context.
+func (conn *Connection) SendWithContext(ctx context.Context, method, extraPath string,
+	params url.Values, headers http.Header, body io.Reader) (*http.Response, error) {
+
 	reqURL := addToURL(conn.URL, extraPath, params)
 
-	req, err := http.NewRequest(method, reqURL, body)
+	req, err := http.NewRequestWithContext(ctx, method, reqURL, body)
 	if err != nil {
 		return nil, fmt.Errorf("fail to create the HTTP %s request: %+v", method, err)
 	}