feat: add Node samples

[ace-n]

~DO NOT MERGE until everyone's in sync on client library initialization (DLP/dlp shenanigans).~

~Note: there are lots of merge conflicts due to whitespace changes. Once we've approved this PR, I can fix those locally and force-push the results to the add-nodejs branch.~

[kurtisvg]

So far LGTM, but there are still quite a few sections missing Node.JS samples. Is this intentional?

[ace-n]

@kurtisvg I was omitting Node samples for the non-Node specific stuff (to reduce maintenance load + visual clutter).

If you'd rather I change that, I'm happy to do so though!

[kurtisvg]

@ace-n I think it make's sense to have a different sample for each language, even if there aren't any major derivations.

[kurtisvg]

Also, maybe tangentially, I noticed that "Node.js" tabs look like they are broken -when I click on one tab it doesn't switch all the Tabs, but it does for "Java". I switched the tabs to "Node" and the tab switching works, but the linting is lost. I switched to "Javascript" and both worked?

[ace-n]

N.B: this is running into merge conflicts due (mostly) to whitespaces. 😬

Once this PR is approved, I'll close it and create a clean version elsewhere (that we can rubber-stamp and merge).

[ace-n]

@sofisl and I chatted about the DLP/dlp issue. We're reluctant to rename DlpServiceClient (because it's exported under that name), but the initialized client object could be named something like dlpClientInstance (instance being the key word here).

@grayside does this address your concerns?

[ace-n]

@sofisl over to you for one final (double-check-y) LGTM. 🙂

Please merge for me once you've approved - thanks!