Specific interface for provider enhancement (1/3)

[colerogers]

Change for the the specific app distro interface. Exposes onNewTesterIosDevicePublished from the v2/alerts/appDistribution namespace

Ex ~

import { onNewTesterIosDevicePublished } from "firebase-functions/v2/alerts/appDistribution";

// newTesterIosDevicePublished interface
export const func = onNewTesterIosDevicePublished((event) => { … });
export const func1 = onNewTesterIosDevicePublished("123456789", (event) => { … });
export const func2 = onNewTesterIosDevicePublished({ appId: "123456789" }, (event) => { … });

[taeold]

mostly lgtm. waiting on some changes to flow from #1020.

[taeold]

lgtm w/ a comment on adding punctuation on public doc strings.

[inlined]