ci: add scheduled workflow to bump productionstack chart dependencies

[zhuangqh]

Reason for Change:
Adds a daily scheduled workflow (06:00 UTC, plus workflow_dispatch) that keeps the productionstack umbrella chart dependencies up to date against MCR (stable X.Y.Z tags only, never downgrades):

• hack/chart-deps.yaml: dependency groups, one PR each on automation/bump-<group>:
  • llm-gateway: llm-gateway-apikey + llm-gateway-azureauth OCI charts
  • body-based-routing: forked subchart, BBR image
  • keda-kaito-scaler: forked subchart, keda-kaito-scaler image
• hack/bump-chart-deps.sh <group>: bumps OCI chart versions, or for forks the image tag / appVersion / README mentions and the subchart version (mirrors the image tag without v), then the umbrella dependency version and Chart.lock.
• .github/workflows/bump-chart-deps.yaml: opens or updates the PR with GITHUB_TOKEN, then dispatches ci.yaml and e2e.yaml on the PR branch (PRs created by GITHUB_TOKEN don't trigger pull_request workflows). CI is dispatched when the PR is created or moves to a new version, not on plain rebases. If the PR branch has manual (non-bot, non-merge) commits, it is left untouched and the workflow comments once per newer version instead.

Also aligns the body-based-routing subchart version with its image: 0.1.1 → 1.5.0 (appVersion v1.5.0), so future bumps keep version and appVersion consistent.

Requirements

• added unit tests and e2e tests (if applicable).

Issue Fixed:

Notes for Reviewers:
No unit tests added; the script was tested locally by pinning older versions for all three groups and checking that it bumped them back to exactly the current tree, plus failure cases (unknown group, missing registry repo). actionlint and shellcheck pass, and helm lint passes after the BBR version change.

To verify after merge (first real run):

• dispatched ci.yaml / e2e.yaml checks satisfy the required e2e-tests and golangci-lint checks on the bot PR;
• require_extra_approval_for_unattributed_changes doesn't block the bot's commits.