Feat. request: timeout for default http client

[pkly]

Is your feature request related to a problem? Please describe.
It is not possible to set a timeout for the default http client.

Describe the solution you'd like
Allow Google/Client to take a timeout option in it's config so it can be passed along to guzzle client during creation of default http client.

Describe alternatives you've considered
Adding PSR http client support instead of using guzzle, as that would possibly fix this issue, but would require some reorganization on the library's part.