feat: reverse shares (#86)

* add first concept

* add reverse share funcionality to frontend

* allow creator to limit share expiration

* moved reverse share in seperate module

* add table to manage reverse shares

* delete complete share if reverse share was deleted

* optimize function names

* add db migration

* enable reverse share email notifications

* fix config variable descriptions

* fix migration for new installations

backend/src/reverseShare/dto/reverseShare.dto.ts

@@ -0,0 +1,18 @@
+import { Expose, plainToClass } from "class-transformer";
+
+export class ReverseShareDTO {
+  @Expose()
+  id: string;
+
+  @Expose()
+  maxShareSize: string;
+
+  @Expose()
+  shareExpiration: Date;
+
+  from(partial: Partial<ReverseShareDTO>) {
+    return plainToClass(ReverseShareDTO, partial, {
+      excludeExtraneousValues: true,
+    });
+  }
+}