docs: make `callback.apiResponse` argument a link to the upstream docs

[stephenplusplus]

continuing from #990 (comment)

Anywhere we document an apiResponse argument, we should be able to link it to the API docs that show what the user can expect from that object.

Tip: for most of the API docs I've seen, you can append a fragment #response to the URL to deep link to the relevant section.

[callmehiphop]

Perhaps this would be better placed in gcloud-common?

[stephenplusplus]

Possibly, but the task will be actually writing link tags in the JSDocs. Unless you can think of an automated way to do this with metadata from the big JSON doc?

[callmehiphop]

Good point, it should probably just be in both.

[stephenplusplus]

We are probably not going to make any changes to our GitHub hosted docs, as our repos start to migrate out onto cloud.google.com.