Livedata filter selectize input for lists does not have a label

First reported by automated tests on CI. The livedata regular filter inputs are labelled since XWIKI-20755 , but somehow the input used in the selectize component used in list filters is not labelled. It could be labelled with the same label as the one used for the hidden input.

```
Validation in the test method [deleteField]
Check for [org.xwiki.xclass.test.po.ClassSheetPage] at http://xwikiweb:8080/xwiki/bin/view/NestedClassEditorIT/deleteField.
Found [1] items

1: Form elements must have labels
Description: Ensure every form element has a label
Help URL: https://dequeuniversity.com/rules/axe/4.10/label?application=axeAPI
Help: Form elements must have labels
Impact: critical
Tags: cat.forms, wcag2a, wcag412, section508, section508.22.n, TTv5, TT5.c, EN-301-549, EN-9.4.1.2, ACT

HTML element:
<input type="text" autocomplete="new-password" autofill="no" tabindex="" style="width: 4px;">
Selector: [input[autocomplete="new-password"]]
Fix any of the following:
Form element does not have an implicit (wrapped) <label>
Form element does not have an explicit <label>
aria-label attribute does not exist or is empty
aria-labelledby attribute does not exist, references elements that do not exist or references elements that are empty
Element has no title attribute
Element has no placeholder attribute
Element's default semantics were not overridden with role="none" or role="presentation"
```