Add template linting via djlint (#25212)

So I found this [linter](https://github.com/Riverside-Healthcare/djlint)
which features a mode for go templates, so I gave it a try and it did
find a number of valid issue, like unbalanced tags etc. It also has a
number of bugs, I had to disable/workaround many issues.

Given that this linter is written in python, this does add a dependency
on `python` >= 3.8 and `poetry` to the development environment to be
able to run this linter locally.

- `e.g.` prefixes on placeholders are removed because the linter had a
false-positive on `placeholder="e.g. cn=Search"` for the `attr=value`
syntax and it's not ideal anyways to write `e.g.` into a placeholder
because a placeholder is meant to hold a sample value.
- In `templates/repo/settings/options.tmpl` I simplified the logic to
not conditionally create opening tags without closing tags because this
stuff confuses the linter (and possibly the reader as well).

templates/admin/queue_manage.tmpl

@@ -44,7 +44,7 @@
 		</h4>
 		<div class="ui attached segment">
 			<p>{{.locale.Tr "admin.monitor.queue.settings.desc"}}</p>
-			<form method="POST" action="{{.Link}}/set">
+			<form method="post" action="{{.Link}}/set">
 				{{$.CsrfTokenHtml}}
 				<div class="ui form">
 					<div class="inline field">