Updated dockerhub image provider to use couchbase/server repo.

We previously used the couchbase:$TAG path to access images, but these are
slightly delayed due to needing DockerHub approval.  We now use the
couchbase/server:$TAG path, which is fully under Couchbase' control.

deployment/dockerdeploy/dockerhubimageprovider.go

@@ -39,7 +39,7 @@ func (p *DockerHubImageProvider) GetImage(ctx context.Context, def *ImageDef) (*
 		serverVersion = fmt.Sprintf("enterprise-%s", def.Version)
 	}
 
-	dhImagePath := fmt.Sprintf("couchbase:%s", serverVersion)
+	dhImagePath := fmt.Sprintf("couchbase/server:%s", serverVersion)
 	p.Logger.Debug("identified dockerhub image to pull", zap.String("image", dhImagePath))
 
 	return MultiArchImagePuller{