Adds v2 test lab triggers

[colerogers]

This change adds test lab triggers to the v2 codebase and sneaks in some remote config changes. For remote config, we update the tsdoc strings for reference docs and remove @Alpha tags since the public docs have been published.

Test Lab functions:

import {
  onTestMatrixCompleted,
  TestMatrixCompletedData
} from "firebase-functions/v2/testLab";

// passing in a handler only
export const fn1 = onTestMatrixCompleted((event) => { ... });

// declaring options
export const fn2 = onTestMatrixCompleted(
  { region: "us-central1", retry: true },
  (event) => {  ...  }
);

[TheIronDev]

Any chance we can change this to not be any | Promise ? (same with others)

[colerogers]

Do you have a better recommendation?

We might be able to get away with void | Promise, but I'd argue it's better to be consistent with the other v2 event providers that all use any | Promise. For example remote config, storage, crashlytics, etc.

Also, we'd probably have to have a followup api review since this has already been approved by council

[TheIronDev]

I guess my main question was along the lines of if we could avoid the any.

But if theres prior art, and would require api review again... I'm alright leave it as-is.

[TheIronDev]

I love all the thoroough documentation!!!