feat: add announcement channels, publishing and following (#3090)

packages/errors/src/domains/channel/MessageAlreadyCrosspostedError.ts

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {APIErrorCodes} from '@fluxer/constants/src/ApiErrorCodes';
+import {BadRequestError} from '@fluxer/errors/src/domains/core/BadRequestError';
+
+export class MessageAlreadyCrosspostedError extends BadRequestError {
+	constructor() {
+		super({
+			code: APIErrorCodes.MESSAGE_ALREADY_CROSSPOSTED,
+		});
+	}
+}