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/files-changed.yml

@@ -15,6 +15,9 @@ on:
       actions:
         description: "whether actions files changed"
         value: ${{ jobs.detect.outputs.actions }}
+      templates:
+        description: "whether templates files changed"
+        value: ${{ jobs.detect.outputs.templates }}
 
 jobs:
   detect:
@@ -27,6 +30,7 @@ jobs:
       frontend: ${{ steps.changes.outputs.frontend }}
       docs: ${{ steps.changes.outputs.docs }}
       actions: ${{ steps.changes.outputs.actions }}
+      templates: ${{ steps.changes.outputs.templates }}
     steps:
       - uses: actions/checkout@v3
       - uses: dorny/paths-filter@v2
@@ -35,7 +39,7 @@ jobs:
           filters: |
             backend:
               - "**/*.go"
-              - "**/*.tmpl"
+              - "templates/**/*.tmpl"
               - "go.mod"
               - "go.sum"
 
@@ -51,3 +55,6 @@ jobs:
 
             actions:
               - ".github/workflows/*"
+
+            templates:
+              - "templates/**/*.tmpl"