Introduce shared template for search inputs (#25338)

- Set
[type=search](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/search)
- Disable spellcheck
- Set maxLength 255 that I found in `templates/repo/issue/search.tmpl`
- Remove unnecessary `max-width`, it does nothing

---------

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Giteabot <teabot@gitea.io>

templates/admin/user/list.tmpl

@@ -51,8 +51,8 @@
 				</div>
 
 				<!-- Search Text -->
-				<div class="ui fluid action input" style="max-width: 70%;">
-					<input name="q" value="{{.Keyword}}" placeholder="{{.locale.Tr "explore.search"}}..." autofocus>
+				<div class="ui fluid action input">
+					{{template "shared/searchinput" dict "locale" .locale "Value" .Keyword "AutoFocus" true}}
 					<button class="ui primary button">{{.locale.Tr "explore.search"}}</button>
 				</div>
 			</form>