refactor frontend-e2e-against-stack to avoid hg-ci token

as part of [#i-2026-05-16-coinbasecartel-claimed-access-to-grafana-data](https://grafanalabs.enterprise.slack.com/archives/C0B4D1WTSUU) we need to remove this common secret `ci/common/hg-ci` used by gha `frontend-e2e-against-stack` in **plugin-ci-workflows** ([here](https://github.com/grafana/plugin-ci-workflows/blob/2ba6cdd6b3dafd2053500b64ff19951dadf1e208/actions/plugins/frontend-e2e-against-stack/action.yml#L149)).
The idea is to pass the provisioning files by input params and each repo should load that info from vault stored on repo level.

Check this PR as a reference: https://github.com/grafana/asserts-app-plugin/pull/3280