feat(tasks): expand subtasks (#2345)

This change adds a parameter to expand subtasks - if provided, Vikunja will ensure all subtasks are present in the results list.

Resolves https://community.vikunja.io/t/subtasks-show-on-different-pages/2292
Reviewed-on: https://kolaente.dev/vikunja/vikunja/pulls/2345
Co-authored-by: kolaente <k@knt.li>
Co-committed-by: kolaente <k@knt.li>

frontend/src/services/taskCollection.ts

@@ -12,6 +12,7 @@ export interface TaskFilterParams {
 	filter_timezone?: string,
 	s: string,
 	per_page?: number,
+	expand?: 'subtasks' | null,
 }
 
 export function getDefaultTaskFilterParams(): TaskFilterParams {
@@ -22,6 +23,7 @@ export function getDefaultTaskFilterParams(): TaskFilterParams {
 		filter_include_nulls: false,
 		filter_timezone: '',
 		s: '',
+		expand: 'subtasks',
 	}
 }