Fix some deprecations and deprecate old backend system

As described here: backstage/community-plugins#1176

Added a deprecation note in the readme as well, and links to the new docs in
the deprecated types and methods.

.changeset/cool-rockets-confess.md

@@ -0,0 +1,13 @@
+---
+'@spreadshirt/backstage-plugin-s3-viewer-backend': patch
+---
+
+Replace some deprecations caused by the removal of the backend-tasks plugin and deprecate old backend system.
+Please, remove any usage of `RouterOptions` and `createRouter`.
+
+The old backend system methods will be completely removed in the next release, so none of the deprecations 
+caused by these functions are going to be addressed.
+
+More info about this process [in this issue](https://github.com/backstage/community-plugins/issues/1176).
+
+To set up the backend using the new backend system, follow [this documentation](https://github.com/spreadshirt/backstage-plugin-s3/tree/main/plugins/s3-viewer-backend#new-backend-system).

plugins/s3-viewer-backend/README.md

@@ -14,6 +14,8 @@ It also includes a permission integration, to restrict access to certain data wi
 
 ## Getting started
 
+> :warning: **This setup is deprecated and will be removed in a future release. Please, use the [new backend system instead](#new-backend-system).**
+
 To get started, follow these steps:
 
 1. Install the plugin by running this command:

plugins/s3-viewer-backend/config.d.ts

@@ -1,4 +1,4 @@
-import { TaskScheduleDefinitionConfig } from '@backstage/backend-tasks';
+import { SchedulerServiceTaskScheduleDefinitionConfig } from '@backstage/backend-plugin-api';
 
 /** Configuration for the S3 Viewer plugin */
 export interface Config {
@@ -7,7 +7,9 @@ export interface Config {
      * If defined, it sets the schedule used to refresh the list of buckets
      * @visibility backend
      * */
-    bucketRefreshSchedule: TaskScheduleDefinitionConfig | undefined;
+    bucketRefreshSchedule:
+      | SchedulerServiceTaskScheduleDefinitionConfig
+      | undefined;
 
     /** @visibility backend */
     bucketLocatorMethods: Array<

plugins/s3-viewer-backend/src/service/router.ts

@@ -35,6 +35,10 @@ import {
   PolicyDecision,
 } from '@backstage/plugin-permission-common';
 
+/**
+ * @deprecated Use the new backend system instead: https://github.com/spreadshirt/backstage-plugin-s3/tree/main/plugins/s3-viewer-backend#new-backend-system
+ * @public
+ */
 export interface RouterOptions {
   logger: LoggerService;
   config: RootConfigService;
@@ -45,6 +49,10 @@ export interface RouterOptions {
   httpAuth?: HttpAuthService;
 }
 
+/**
+ * @deprecated Use the new backend system instead: https://github.com/spreadshirt/backstage-plugin-s3/tree/main/plugins/s3-viewer-backend#new-backend-system
+ * @public
+ */
 export async function createRouter(
   options: RouterOptions,
 ): Promise<express.Router> {