Update hashicorp/terraform

[ialidzhikov]

/kind enhancement

terraform@0.12.29 is not able to fetch the latest versions of the terraform providers:

$ terraform-0.12.29 init

Initializing the backend...

Initializing provider plugins...
- Checking for available provider plugins...

No provider "aws" plugins meet the constraint "3.43.0".

The version constraint is derived from the "version" argument within the
provider "aws" block in configuration. Child modules may also apply
provider version constraints. To view the provider versions requested by each
module in the current configuration, run "terraform providers".

To proceed, the version constraints for this provider must be relaxed by
either adjusting or removing the "version" argument in the provider blocks
throughout the configuration.


Warning: registry.terraform.io: This version of Terraform has an outdated GPG key and is unable to verify new provider releases. Please upgrade Terraform to at least 0.12.31 to receive new provider updates. For details see: https://discuss.hashicorp.com/t/hcsec-2021-12-codecov-security-event-and-hashicorp-gpg-key-exposure/23512



Error: no suitable version is available

For more details about the issue, see https://discuss.hashicorp.com/t/terraform-updates-for-hcsec-2021-12/23570.

This PR updates the terraform version to 0.12.31 that has the updated public keys and can fetch even the new versions of the terraform providers.

Required for gardener/gardener-extension-provider-aws#319

Release note:

The terraform version for the alicloud, all, aws, azure, gcp, openstack, slim images is updated:
- hashicorp/terraform: 0.12.29 -> 0.12.31

[timebertt]

/lgtm
/test

cc @kon-angelo, maybe the upgrade issues you encountered are related to this?

[timebertt]

Merging, as the TM bot is currently having troubles. We still have the release test