ci: add shared-actions autoupdate and move to Go 1.26

Add the autoupdate workflow that calls the shared go-autoupdate workflow.
Set the Go version to 1.26 in the CI, release and Docker builds.
Update actions/checkout to v6 in the helm chart job.

.github/workflows/autoupdate.yaml

@@ -0,0 +1,20 @@
+name: Autoupdate go.mod and go.sum
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 3 * * *"
+
+permissions:
+  contents: write
+  actions: write
+  pull-requests: write
+  security-events: write
+
+jobs:
+  autoupdate:
+    uses: lukaszraczylo/shared-actions/.github/workflows/go-autoupdate.yaml@main
+    with:
+      go-version: ">=1.26"
+      release-workflow: "release.yaml"
+    secrets: inherit