sia: setup docker with sia-antfarm for test #4514

Always pull the latest Sia Antfarm docker image
Add wait for Sia renter to become upload ready

Co-authored-by: Filip Rysavy <fil@siasky.net>

backend/sia/sia.go

@@ -4,8 +4,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"github.com/rclone/rclone/fs/config"
-	"github.com/rclone/rclone/lib/encoder"
 	"io"
 	"net/http"
 	"net/url"
@@ -13,6 +11,9 @@ import (
 	"strings"
 	"time"
 
+	"github.com/rclone/rclone/fs/config"
+	"github.com/rclone/rclone/lib/encoder"
+
 	"github.com/pkg/errors"
 	"github.com/rclone/rclone/backend/sia/api"
 	"github.com/rclone/rclone/fs"