Implement a hook allowing enterprise modules to perform actions on startup

Add an interface `io.element.android.features.enterprise.api.AppStartupHook`,
which can be implemented in the enterprise build to perform certain actions on
startup.

It's a bit of a kludge for now since it doesn't block the rest of the app from
proceeding, but it will serve our purposes for now.

app/src/main/kotlin/io/element/android/x/MainActivity.kt

@@ -61,6 +61,13 @@ class MainActivity : NodeActivity() {
         setContent {
             MainContent(appBindings)
         }
+
+        val activity = this
+        appBindings.appStartupHooks().forEach {
+            lifecycleScope.launch {
+                it.onAppStartup(activity)
+            }
+        }
     }
 
     @Composable

app/src/main/kotlin/io/element/android/x/di/AppBindings.kt

@@ -10,7 +10,9 @@ package io.element.android.x.di
 
 import dev.zacsweers.metro.AppScope
 import dev.zacsweers.metro.ContributesTo
+import dev.zacsweers.metro.Multibinds
 import io.element.android.features.api.MigrationEntryPoint
+import io.element.android.features.enterprise.api.AppStartupHook
 import io.element.android.features.enterprise.api.EnterpriseService
 import io.element.android.features.lockscreen.api.LockScreenEntryPoint
 import io.element.android.features.lockscreen.api.LockScreenService
@@ -51,4 +53,7 @@ interface AppBindings {
     fun buildMeta(): BuildMeta
 
     fun sentrySdkDsn(): SentrySdkDsn?
+
+    @Multibinds(allowEmpty = true)
+    fun appStartupHooks(): Set<AppStartupHook>
 }