Migrate configuration of UptimeRobot to as-code

We now have quite a lot of configuration in UptimeRobot, and no central place to trace why things are configured as they are, and no way to quickly ensure configuration is consistent.

This is typically the driver to move to an "as-code" approach, where configuration is stored in a repository to ensure changes traceability and also where common configuration is more clearly expressed thanks to modular approaches.

I feel like we should take some time to consider an "as-code" approach for UptimeRobot configuration

We could for instance:
- leverage Terraform to deploy our configuration changes
- leverage Github Actions to avoid every Ops to need to have Terraform installed locally

@rgaudin @kelson42 WDYT?

No files or tests are named. Start by inventorying the existing UptimeRobot configuration, then evaluate Terraform for managing it and GitHub Actions for applying changes; done means the configuration has a documented, repeatable as-code workflow.

Written by the indexing model from the issue text.