Add config for charmed-openstack-exporter-snap

[gabrielcocenza]

This moves the following files for https://github.com/canonical/charmed-openstack-exporter-snap under control of this automation repo:

• CODEOWNERS
• workflows/promote.yaml
• workflows/release.yaml

It will also apply our standard config to the charmed-openstack-exporter-snap repository itself.

Additional features:

• workflow_dispatch for release
• choose to include the check or not for release

[gabrielcocenza]

Closing because this doesn't work with forked repo