chore: add lefthook config for make docs

Adds lefthook config to .kres.yaml, for the custom.Step that generates
the `make docs` target.

Signed-off-by: Maja Bojarska <maja.bojarska@siderolabs.com>

Author: majabojarska

.kres.yaml

@@ -721,6 +721,17 @@ spec:
   ghaction:
     enabled: true
     condition: on-pull-request
+  lefthook:
+    enabled: true
+    hooks:
+      pre-commit:
+        jobs:
+          - name: fix
+            group:
+              jobs:
+                - name: docs
+                  run: make docs
+                  stage_fixed: true
 ---
 kind: custom.Step
 name: talosctl