Add options for high volume endpoint and api version

[KMarkert]

Right now the endpoint urls are hard coded at a couple of places (e.g. https://developers.google.com/earth-engine/cloud/highvolume?hl=en#using-the-high-volume-endpoint).

There needs to be an option to allow for the different api versions (i.e. v1alpha vs v1beta) as well as the high-volume endpoint to allow users different options when using package.