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/repo/commit_page.tmpl

@@ -19,7 +19,7 @@
 		{{end}}
 		<div class="ui top attached header clearing segment gt-relative commit-header {{$class}}">
 			<div class="gt-df gt-mb-4 gt-fw">
-				<h3 class="gt-mb-0 gt-f1"><span class="commit-summary" title="{{.Commit.Summary}}">{{RenderCommitMessage $.Context .Commit.Message $.RepoLink $.Repository.ComposeMetas}}</span>{{template "repo/commit_statuses" dict "Status" .CommitStatus "Statuses" .CommitStatuses  "root" $}}</h3>
+				<h3 class="gt-mb-0 gt-f1"><span class="commit-summary" title="{{.Commit.Summary}}">{{RenderCommitMessage $.Context .Commit.Message $.RepoLink $.Repository.ComposeMetas}}</span>{{template "repo/commit_statuses" dict "Status" .CommitStatus "Statuses" .CommitStatuses "root" $}}</h3>
 				{{if not $.PageIsWiki}}
 					<div>
 						<a class="ui primary tiny button" href="{{.SourcePath}}">
@@ -70,7 +70,7 @@
 												"branchForm" "branch-dropdown-form"
 												"branchURLPrefix" (printf "%s/_cherrypick/%s/" $.RepoLink .CommitID) "branchURLSuffix" ""
 												"setAction" true "submitForm" true}}
-											<form method="GET" action="{{$.RepoLink}}/_cherrypick/{{.CommitID}}/{{if $.BranchName}}{{PathEscapeSegments $.BranchName}}{{else}}{{PathEscapeSegments $.Repository.DefaultBranch}}{{end}}" id="branch-dropdown-form">
+											<form method="get" action="{{$.RepoLink}}/_cherrypick/{{.CommitID}}/{{if $.BranchName}}{{PathEscapeSegments $.BranchName}}{{else}}{{PathEscapeSegments $.Repository.DefaultBranch}}{{end}}" id="branch-dropdown-form">
 												<input type="hidden" name="ref" value="{{if $.BranchName}}{{$.BranchName}}{{else}}{{$.Repository.DefaultBranch}}{{end}}">
 												<input type="hidden" name="refType" value="branch">
 												<input type="hidden" id="cherry-pick-type" name="cherry-pick-type"><br>