feat(ci): add scheduled auto-release workflow

Introduce a cron-triggered auto-release workflow that runs on the second Sunday of each month,
creating a time-based tag in YYYY-MM format and dispatching the release workflow.

The release workflow is extended with a workflow_dispatch trigger accepting a tag input, so it can be
invoked both by tag pushes and programmatically by the auto-release. Version extraction is unified
via a dedicated step using `inputs.tag || github.ref_name` in both jobs.

Co-authored-by: Copilot <copilot@github.com>

renovate.json

@@ -0,0 +1,9 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "local>volker.raschek/renovate-config:default#master",
+    "local>volker.raschek/renovate-config:container#master",
+    "local>volker.raschek/renovate-config:actions#master",
+    "local>volker.raschek/renovate-config:regexp#master"
+  ]
+}