EPIC: Maintenance pages

[mrnicegyu11]

To have a maintenance page even if the docker swarm is down or machines are down, a machine hosting the nginx-based maintenance page needs to be added to the load-balancing.

On aws:

• Add a dedicated ultra-small machine, or even better, a lambda, which only shows the maintenance page. This is added to the osparc.io and staging.osparc.io loadbalancer.

On dalco:

• Request a VM, or if impossible, a shitty old machine
• Provision with keepalived (as found in osparc-infra/ansible) to share the Floating IP
• Have it run only the maintenance page

On master:

• We dont need it for now

### Tasks
- [ ] https://github.com/ITISFoundation/osparc-ops-environments/issues/325
- [ ] https://github.com/ITISFoundation/osparc-ops-environments/issues/214
- [ ] https://github.com/ITISFoundation/osparc-ops-environments/issues/409
- [x] Add FloatingIP maintenance page for dalco with VM from O+P
- [x] Audit ansible provisioning of maintenance VM machines

[YuryHrytsuk]

This is done for NIH / DALCO / TIP / Sim4life PROD