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/keys_gpg.tmpl

@@ -18,7 +18,7 @@
 					<p>{{.locale.Tr "settings.gpg_token_required"}}</p>
 				</div>
 				<div class="field">
-					<label for="token">{{.locale.Tr "settings.gpg_token"}}
+					<label for="token">{{.locale.Tr "settings.gpg_token"}}</label>
 					<input readonly="" value="{{.TokenToSign}}">
 					<div class="help">
 						<p>{{.locale.Tr "settings.gpg_token_help"}}</p>

templates/user/settings/packages.tmpl

@@ -21,5 +21,4 @@
 			</div>
 		</div>
 	</div>
-</div>
 {{template "user/settings/layout_footer" .}}

templates/user/settings/repos.tmpl

@@ -42,7 +42,7 @@
 													<div class="content">
 														<p>{{$.locale.Tr "repo.adopt_preexisting_content" $dir}}</p>
 													</div>
-													<form class="ui form" method="POST" action="{{AppSubUrl}}/user/settings/repos/unadopted">
+													<form class="ui form" method="post" action="{{AppSubUrl}}/user/settings/repos/unadopted">
 														{{$.CsrfTokenHtml}}
 														<input type="hidden" name="id" value="{{$dir}}">
 														<input type="hidden" name="action" value="adopt">
@@ -59,7 +59,7 @@
 													<div class="content">
 														<p>{{$.locale.Tr "repo.delete_preexisting_content" $dir}}</p>
 													</div>
-													<form class="ui form" method="POST" action="{{AppSubUrl}}/user/settings/repos/unadopted">
+													<form class="ui form" method="post" action="{{AppSubUrl}}/user/settings/repos/unadopted">
 														{{$.CsrfTokenHtml}}
 														<input type="hidden" name="id" value="{{$dir}}">
 														<input type="hidden" name="action" value="delete">

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}}">