Bring back .withDefaultParam

[ryanseys]

@proppy found the feature useful. Used to set default params for every request. I always thought it was more unpredictable so it was never transitioned to the new library.

See discussion: https://github.com/GoogleCloudPlatform/google-cloud-datastore/pull/47/files#r17020602

[proppy]

Maybe this could be make more predictable by making those params immutable, for example they could be passed to the client initializer function.

[ryanseys]

Yes this the only place I would condone putting the change.

What are your thoughts on something like the following:

var google = require('googleapis');
var datastore = google.datastore({ 
  version: 'v1beta2', 
  defaultParams: { datasetId: 'abc123' }, 
  auth: auth 
});

[ryanseys]

Or instead of defaultParams: a less verbose defaults: key?

[proppy]

Maybe just params them. Since those are parameters that will get passed on each request.

[ryanseys]

Yes, params would work.