chore(notifications): Update starter platform code to use existing app (#93614)

We probably don't need two apps where one manages a subset of the other.
This will make things a tiny bit more colocated.

Author: leeandher

src/sentry/conf/server.py

@@ -408,7 +408,6 @@ def env(
     "sentry.sentry_apps",
     "sentry.integrations",
     "sentry.notifications",
-    "sentry.notifications.platform",
     "sentry.flags",
     "sentry.monitors",
     "sentry.uptime",

src/sentry/notifications/apps.py

@@ -5,4 +5,12 @@ class Config(AppConfig):
     name = "sentry.notifications"
 
     def ready(self):
-        pass
+        # Register the NotificationProviders for the platform
+        from sentry.notifications.platform.discord.provider import (  # NOQA
+            DiscordNotificationProvider,
+        )
+        from sentry.notifications.platform.email.provider import EmailNotificationProvider  # NOQA
+        from sentry.notifications.platform.msteams.provider import (  # NOQA
+            MSTeamsNotificationProvider,
+        )
+        from sentry.notifications.platform.slack.provider import SlackNotificationProvider  # NOQA

src/sentry/notifications/platform/README.md

@@ -13,4 +13,4 @@ To register a new provider:
 3. Create a provider module in the new directory.
    - Extend `NotificationProvider` from [`.provider`](./provider.py) and implement its methods/variables.
    - Import `provider_registry` from [`.registry`](./registry.py) and add it via decorator: `@provider_registry.register(<YOUR-KEY-HERE>)`
-4. In [.apps](./apps.py), explicitly import the module to register the provider on initialization.
+4. In [../apps](../apps.py), explicitly import the module to register the provider on initialization.