Optimize metadata queries (#7013)

In this PR:

1. Refactor guards to avoid duplicated queries: WorkspaceAuthGuard and
UserAuthGuard only check for existence of workspace and user in the
request without querying the database

packages/twenty-server/src/engine/guards/workspace-auth.guard.ts

@@ -0,0 +1,15 @@
+import { CanActivate, ExecutionContext } from '@nestjs/common';
+import { GqlExecutionContext } from '@nestjs/graphql';
+
+import { Observable } from 'rxjs';
+
+export class WorkspaceAuthGuard implements CanActivate {
+  canActivate(
+    context: ExecutionContext,
+  ): boolean | Promise<boolean> | Observable<boolean> {
+    const ctx = GqlExecutionContext.create(context);
+    const request = ctx.getContext().req;
+
+    return request.workspace !== undefined;
+  }
+}