Feature request: To have backup server information in case main is unhealthy

What's the feature

So, this is related to this issue # https://github.com/qdm12/gluetun/wiki/Healthcheck

[healthcheck] unhealthy: cannot dial: dial tcp4 104.16.133.229:443: i/o timeout

As the steps provided on that guide, issues sometimes happen on the vpn side, yes, and seems only to change the server information will fix the issue.

Maybe if we can add backup vpn server info on the gluetun side in the docker compose so it can switch to the backup when the main is having the issue? That would be awesome

Extra information and references

For example to have the docker compose in # https://github.com/qdm12/gluetun/wiki/Private-internet-access

Something like:

      - SERVER_REGIONS_Primary=Netherlands
      - SERVER_REGIONS_BACKUP=CA Toronto

In case can't establish the connection to the primary, that can failover to the backup without getting stuck in a loop unhealthy and healthy issue