Admin user search

[SychO9]

Description
The user list on the admin panel currently shows all users ordered by ID. It would be a big improvement to be able to search through it based on username and use the available search gambits. (https://flarum.test/admin#/users)

What needs to be done
The logic/endpoint for searching on the backend is already available, so we just need to hit the API with a search query from the frontend.

• First, we need to add the search input above the table (

  framework/framework/core/js/src/admin/components/UserListPage.tsx

  Line 94 in 0e2053d

  <p class="UserListPage-totalUsers">{app.translator.trans('core.admin.users.total_users', { count: this.userCount })}</p>,

  )
• Then we need the input to store the updated value on a state variable, we an use a Stream property and the bidi attribute for that, here's an example with the nameSingular input value:

  framework/framework/core/js/src/admin/components/EditGroupModal.tsx

  Line 74 in cf818aa

  <input className="FormControl" placeholder={app.translator.trans('core.admin.edit_group.singular_placeholder')} bidi={this.nameSingular} />

• Finally, we need to add the input value to the query (

  framework/framework/core/js/src/admin/components/UserListPage.tsx

  Lines 340 to 345 in 0e2053d

  	app.store
  	.find<User[]>('users', {
  	page: {
  	limit: this.numPerPage,
  	offset: pageNumber * this.numPerPage,
  	},

  ) it would need to be under filter: { q: query }
• We might need to set a debounce to prevent xhr requests from firing too fast when typing.