How to send Custom Headers - No-Cache for example?

How to send headers with metadata to disable the default 1 hour caching of uploaded files to GCS?

**Standard Example**

'Content-Type' => 'text/json',
'acl' => 'public-read',
'enable_cache' => false,
'read_cache_expiry_seconds' => 0,
'Cache-Control' => 'private, max-age=0,no-transform'

**Usecase**
We use Google Cloud Storage as repositories for various web-apps on GAE that often need to have certain specific images/json files modified quickly without having to wait 1 hour until the cache clears (_like on regular filesystems_).

I know applications like `rclone` offers a `--header-upload ` flag with GCS already so it should be possible?

Have i missed something in the documentation?

Thanks for a great plugin!