Upgrade Terraform and providers one step at a time

Upgrading Terraform, three providers and two modules in one pull request makes any surprise in the plan impossible to trace. Treat upgrades like any other change: small, planned and reviewed.

A steady routine:

1. Read the upgrade notes or changelog for the version you are moving to.
2. Change one thing: the Terraform version, or one provider, or one module.
3. Run terraform init -upgrade and terraform plan.
4. Expect no changes in the plan for a pure upgrade. Any change is either a new default or a bug, and should be understood before you apply.
5. Commit the updated lock file with the constraint change.