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).

.github/workflows/pull-compliance.yml

@@ -26,6 +26,19 @@ jobs:
         env:
           TAGS: bindata sqlite sqlite_unlock_notify
 
+  lint-templates:
+    if: needs.files-changed.outputs.templates == 'true'
+    needs: files-changed
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+        with:
+          python-version: "3.11"
+      - run: pip install poetry
+      - run: make deps-py
+      - run: make lint-templates
+
   lint-go-windows:
     if: needs.files-changed.outputs.backend == 'true' || needs.files-changed.outputs.actions == 'true'
     needs: files-changed