Move HTTP service to public for plugin use (#27284)

* Move httpservice for use in plugins

* Adapt httpservice for plugin use

* Fix lint

server/platform/services/marketplace/client.go

@@ -13,7 +13,7 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/mattermost/mattermost/server/public/model"
-	"github.com/mattermost/mattermost/server/v8/platform/services/httpservice"
+	"github.com/mattermost/mattermost/server/public/shared/httpservice"
 )
 
 // Client is the programmatic interface to the marketplace server API.