ci: add on-demand Create Chart Release PR workflow

[gnanirahulnutakki]

Add on-demand chart release workflow

Adds .github/workflows/release-chart-pr.yml — a workflow_dispatch helper to cut chart releases without hand-editing Chart.yaml.

What it does

From Actions -> Create Chart Release PR -> Run workflow, you pick:

• chart — sdc, sdc-client, eoc, or sss
• version — new semver (e.g. 1.4.0, or 1.4.0-rc.1)
• app_version — optional; defaults to version (image tag = chart appVersion)
• base_branch — optional; defaults to master (set this for stacked releases)

It then bumps version + appVersion in that chart's Chart.yaml, creates branch <chart>/<version>, and opens a release PR.

Why a PR (not a direct release)

The existing release.yml (helm/chart-releaser-action) already fires on push to master and cuts the tag + GitHub release + gh-pages index. This workflow just automates the version-bump PR half of the current manual flow, so review + the lint-test-* checks still run before anything is released.

Safety

• Validates version is semver and app_version has no unexpected characters.
• Only rewrites the column-0 version: / appVersion: keys (dependency versions and apiVersion are untouched).
• Fails if the target branch already exists.
• Inputs are passed via env: (not interpolated into the shell) to avoid injection.