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/createReverseShare.dto.ts

@@ -0,0 +1,12 @@
+import { IsBoolean, IsString } from "class-validator";
+
+export class CreateReverseShareDTO {
+  @IsBoolean()
+  sendEmailNotification: boolean;
+
+  @IsString()
+  maxShareSize: string;
+
+  @IsString()
+  shareExpiration: string;
+}