Add yamllint (#26965)

So that https://github.com/go-gitea/gitea/pull/26964 does not happen
again. Merge this after that PR. Config is based on
[node's](https://github.com/nodejs/node/blob/main/.yamllint.yaml).

---------

Co-authored-by: techknowlogick <techknowlogick@gitea.com>

.github/ISSUE_TEMPLATE/feature-request.yaml

@@ -2,23 +2,23 @@ name: Feature Request
 description: Got an idea for a feature that Gitea doesn't have currently?  Submit your idea here!
 labels: ["kind/proposal"]
 body:
-- type: markdown
-  attributes:
-    value: |
-      1. Please speak English, this is the language all maintainers can speak and write.
-      2. Please ask questions or configuration/deploy problems on our Discord
-         server (https://discord.gg/gitea) or forum (https://discourse.gitea.io).
-      3. Please take a moment to check that your feature hasn't already been suggested.
-- type: textarea
-  id: description
-  attributes:
-    label: Feature Description
-    placeholder: |
-      I think it would be great if Gitea had...
-  validations:
-    required: true
-- type: textarea
-  id: screenshots
-  attributes:
-    label: Screenshots
-    description: If you can, provide screenshots of an implementation on another site e.g. GitHub
+  - type: markdown
+    attributes:
+      value: |
+        1. Please speak English, this is the language all maintainers can speak and write.
+        2. Please ask questions or configuration/deploy problems on our Discord
+           server (https://discord.gg/gitea) or forum (https://discourse.gitea.io).
+        3. Please take a moment to check that your feature hasn't already been suggested.
+  - type: textarea
+    id: description
+    attributes:
+      label: Feature Description
+      placeholder: |
+        I think it would be great if Gitea had...
+    validations:
+      required: true
+  - type: textarea
+    id: screenshots
+    attributes:
+      label: Screenshots
+      description: If you can, provide screenshots of an implementation on another site e.g. GitHub