feat(issue-search): support query syntax (#9109)

List of currently supported filters:

- `is:open` (or `-is:closed`)
- `is:closed` (or `-is:open`)
- `is:all`
- `author:<username>`
- `assignee:<username>`
- `review:<username>`
- `mentions:<username>`
- `modified:[>|<]<date>`, where `<date>` is the last update date.
- `sort:<by>:[asc|desc]`, where `<by>` is among
	- created
	- comments
	- updated
	- deadline

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/9109
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Reviewed-by: Ellen Εμιλία Άννα Zscheile <fogti@noreply.codeberg.org>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Shiny Nematoda <snematoda.751k2@aleeas.com>
Co-committed-by: Shiny Nematoda <snematoda.751k2@aleeas.com>

web_src/css/repo/list-header.css

@@ -18,6 +18,7 @@
   align-items: center;
   flex-wrap: wrap;
   justify-content: center;
+  gap: .5rem;
   min-width: 200px; /* to enable flexbox wrapping on mobile */
 }