feat: add support for alerts

[Salakar]

Testing

Deployed one of each function type to ensure they deploy correctly:

from firebase_functions import alerts_fn
from firebase_functions.alerts import app_distribution_fn
from firebase_functions.alerts import billing_fn
from firebase_functions.alerts import crashlytics_fn
from firebase_functions.alerts import performance_fn


@alerts_fn.on_alert_published(alert_type=alerts_fn.AlertType.BILLING_PLAN_UPDATE
                             )
def onalertpublished(
    alert: alerts_fn.AlertEvent[alerts_fn.FirebaseAlertData[
        billing_fn.PlanUpdatePayload]]
) -> None:
    print(alert)


@app_distribution_fn.on_in_app_feedback_published()
def appdistributioninappfeedback(
        alert: app_distribution_fn.InAppFeedbackEvent) -> None:
    print(alert)


@app_distribution_fn.on_new_tester_ios_device_published()
def appdistributionnewrelease(
        alert: app_distribution_fn.NewTesterDeviceEvent) -> None:
    print(alert)


@billing_fn.on_plan_automated_update_published()
def billingautomatedplanupdate(
        alert: billing_fn.BillingPlanAutomatedUpdateEvent) -> None:
    print(alert)


@billing_fn.on_plan_update_published()
def billingplanupdate(alert: billing_fn.BillingPlanUpdateEvent) -> None:
    print(alert)


@crashlytics_fn.on_new_fatal_issue_published()
def crashlyticsnewfatalissue(
        alert: crashlytics_fn.CrashlyticsNewFatalIssueEvent) -> None:
    print(alert)


@crashlytics_fn.on_new_nonfatal_issue_published()
def crashlyticsnewnonfatalissue(
        alert: crashlytics_fn.CrashlyticsNewNonfatalIssueEvent) -> None:
    print(alert)


@crashlytics_fn.on_new_anr_issue_published()
def crashlyticsnewanrissue(
        alert: crashlytics_fn.CrashlyticsNewAnrIssueEvent) -> None:
    print(alert)


@crashlytics_fn.on_regression_alert_published()
def crashlyticsregression(
        alert: crashlytics_fn.CrashlyticsRegressionAlertEvent) -> None:
    print(alert)


@crashlytics_fn.on_stability_digest_published()
def crashlyticsstabilitydigest(
        alert: crashlytics_fn.CrashlyticsStabilityDigestEvent) -> None:
    print(alert)


@crashlytics_fn.on_velocity_alert_published()
def crashlyticsvelocity(
        alert: crashlytics_fn.CrashlyticsVelocityAlertEvent) -> None:
    print(alert)


@performance_fn.on_threshold_alert_published()
def performancethreshold(
        alert: performance_fn.PerformanceThresholdAlertEvent) -> None:
    print(alert)

All functions deployed without issue:

Firebase console shows the correct fn types for each:

Billing plan update fn triggers with correct payload when upgrading/downgrading a Firebase project: