feat: implement Markdown and HTML page imports (#85)

* page import feature
* make file interceptor common

* replace @tiptap/html
* update tiptap version

* reduce table margin

* update tiptap version

* switch to upstream drag handle lib (fixes table dragging)

* WIP

* Page import module and other fixes

* working page imports

* extract page title from h1 heading

* finalize page imports

* cleanup unused imports

* add menu arrow

apps/server/src/common/interceptors/file.interceptor.ts

@@ -0,0 +1,25 @@
+import {
+  Injectable,
+  NestInterceptor,
+  ExecutionContext,
+  CallHandler,
+  BadRequestException,
+} from '@nestjs/common';
+import { Observable } from 'rxjs';
+import { FastifyRequest } from 'fastify';
+
+@Injectable()
+export class FileInterceptor implements NestInterceptor {
+  public intercept(
+    context: ExecutionContext,
+    next: CallHandler,
+  ): Observable<any> {
+    const req: FastifyRequest = context.switchToHttp().getRequest();
+
+    if (!req.isMultipart() || !req.file) {
+      throw new BadRequestException('Invalid multipart content type');
+    }
+
+    return next.handle();
+  }
+}