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/shared/actions/runner_list.tmpl

@@ -65,7 +65,7 @@
 						<td>{{.ID}}</td>
 						<td><p data-tooltip-content="{{.Description}}">{{.Name}}</p></td>
 						<td>{{if .Version}}{{.Version}}{{else}}{{$.locale.Tr "unknown"}}{{end}}</td>
-						<td><span data-tooltip-content="{{.BelongsToOwnerName}}">{{.BelongsToOwnerType.LocaleString $.locale}}<span></td>
+						<td><span data-tooltip-content="{{.BelongsToOwnerName}}">{{.BelongsToOwnerType.LocaleString $.locale}}</span></td>
 						<td class="runner-tags">
 							{{range .AgentLabels}}<span class="ui label">{{.}}</span>{{end}}
 						</td>