Workflow for installing/upgrading secrets chart

[jpopelka]

created in a PR for #13

The secrets/values to be passed to the chart will be stored in Environments secrets (discuss with the team whether everyone's OK with this)

Inspiration:

• https://github.com/packit/helm/blob/main/.github/workflows/deploy-import-images.yml

EDIT: I found this useful when working on #12