Sync `jws_private_key` between all app servers

Zendesk: https://gitlab.zendesk.com/agent/tickets/79645

The person that contributed the OpenID Connect feature reported that GitLab.com is returning a different key for each request, presumably because the app servers don't have the private key synced. We should sync jws_private_key in gitlab-secrets.json across all nodes.

See gitlab-org/omnibus-gitlab!1222 (diffs) for where this was implemented.