Create x-goog-api-client header for Translation, BigQuery, and Storage

[bjwatson]

What

We need to add the following HTTP header to methods in the Translation, BigQuery, and Storage client libraries:

x-goog-api-client: "gl-node/{NodeJS version} gccl/{client library version}"

Why

This is most critical for Translation, because we discovered that we have no other way of tracking its usage. While we're at it, let's get this done for BigQuery and Storage, too.

This is P0 because every day this is not done is another day of data that we lose. Plus it will take time for users to upgrade to the versions of the client libraries in which this has been done.

[bjwatson]

@stephenplusplus I think that @lukesneeringer has discussed this with you already. I'm belatedly creating the issue to track its completion. Please note that this is P0.

[lukesneeringer]

@stephenplusplus Confirming: please do this as your next task. Thank you.

[stephenplusplus]

When you see a label rainbow, you know it's serious. PR sent: #2223

[bjwatson]

Fo' sho'. Thanks Stephen!