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/user/settings/security/openid.tmpl

@@ -28,7 +28,6 @@
 							{{$.locale.Tr "settings.show_openid"}}
 							</button>
 						{{end}}
-						</button>
 						</form>
 					</div>
 					<div class="content">

templates/user/settings/security/twofa_enroll.tmpl

@@ -6,8 +6,8 @@
 		<div class="ui attached segment">
 			<p>{{.locale.Tr "settings.scan_this_image"}}</p>
 			<img src="{{.QrUri}}" alt="{{.TwofaSecret}}">
-			<p>{{.locale.Tr "settings.or_enter_secret" .TwofaSecret}}
-			<p>{{.locale.Tr "settings.then_enter_passcode"}}
+			<p>{{.locale.Tr "settings.or_enter_secret" .TwofaSecret}}</p>
+			<p>{{.locale.Tr "settings.then_enter_passcode"}}</p>
 			<form class="ui form" action="{{.Link}}" method="post">
 				{{.CsrfTokenHtml}}
 				<div class="inline required field {{if .Err_Passcode}}error{{end}}">