vault_concourse: store worker approle secret in vault

Currently the configuration concourse-workers uses a remote state to retrieve this secret.

We want to get rid of this remote state as its very fragile since terraform version must be kepy in sync between keycloak-vault-infra, keycloak-vault-cloud and concourse-workers.

First step is to store the workers approle secret in vault at secret/zones/fe/ZONE_NAME/CONCOURSE_ROLE_NAME-worker

When deployed everywhere concourse-workers configuration could add a vault provider on the current zone (or parent zone for client zones) and pull this secret to configure the worker instead of using the remote state.