Upgrade pattern for handling blackbox exporter CA in older hosts

[hellais]

Older hosts are using ooca_ca to generate the certificates used by the prometheus scraper to collect blackbox exported metrics.

Newer hosts are handling this "on the fly", like this: https://github.com/ooni/sysadmin/blob/master/ansible/roles/base-bullseye/tasks/main.yml#L219.

https://github.com/ooni/sysadmin/blob/master/ansible/roles/base-bullseye/tasks/main.yml#L229 <--- this deploys the updated cert to all hosts sending data to vector without running a full host bootstrap

We should update the old hosts to make use of this new pattern.

[hellais]

This was leading to the following error when running the node exporter scrape:

As a hotfix we just put in the tls_config section the following:

    tls_config:
      # XXX this is a hotfix to https://github.com/ooni/backend/issues/747
      insecure_skip_verify: true