Implemented CanOverwriteFiles to spare unnecessary calls to GCS

[mhlavac]

Implemented CanOverwriteFiles to spare unnecessary calls to GCS

Filesystem will skip has check if adapter implements CanOverwriteFiles, when dealing with a lot of files this can lead to 50% less requests and up to 50% speed increase.

From Filesystem:

    /**
     * @inheritdoc
     */
    public function put($path, $contents, array $config = [])
    {
        $path = Util::normalizePath($path);
        $config = $this->prepareConfig($config);

        if ( ! $this->adapter instanceof CanOverwriteFiles && $this->has($path)) {
            return (bool) $this->getAdapter()->update($path, $contents, $config);
        }

        return (bool) $this->getAdapter()->write($path, $contents, $config);
    }

[RoofTurkey]

Looks good to me! Would be nice to have this implemented