feat: suspend instance improvements (#13861)

* feat(backend): dead instance detection

* feat(backend): suspend type detection

* feat(frontend): show suspend reason on frontend

* feat(backend): resume federation automatically if the server is automatically suspended

* docs(changelog): 配信停止まわりの改善

* lint: fix lint errors

* Update packages/frontend/src/pages/instance-info.vue

* lint: fix lint error

* chore: suspendedState => suspensionState

---------

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

packages/backend/src/models/Instance.ts

@@ -81,13 +81,22 @@ export class MiInstance {
 	public isNotResponding: boolean;
 
 	/**
-	 * このインスタンスへの配信を停止するか
+	 * このインスタンスと不通になった日時
+	 */
+	@Column('timestamp with time zone', {
+		nullable: true,
+	})
+	public notRespondingSince: Date | null;
+
+	/**
+	 * このインスタンスへの配信状態
 	 */
 	@Index()
-	@Column('boolean', {
-		default: false,
+	@Column('enum', {
+		default: 'none',
+		enum: ['none', 'manuallySuspended', 'goneSuspended', 'autoSuspendedForNotResponding'],
 	})
-	public isSuspended: boolean;
+	public suspensionState: 'none' | 'manuallySuspended' | 'goneSuspended' | 'autoSuspendedForNotResponding';
 
 	@Column('varchar', {
 		length: 64, nullable: true,