Chore: update context.tf, build-harness assets

[korenyoni]

what

• Update context.tf.
• Update build-harness assets by running make github/init.
• Clean up unused providers.
• Drop Terraform support prior to 0.13.

why

• The latest version of context.tf (null-label:0.25.0), contains new labels. A module instantiating this module with version 0.25.0 of null-label and making use of new labels will not be able to use this module.
• Running make github/init updates build-harness assets, which includes GitHub Actions Workflows and related files.
• The latest distribution of context.tf (null-label:0.25.0) is not compatible with Terraform 0.12.* because it makes use of validation blocks.

references

• https://github.com/cloudposse/terraform-null-label/releases/tag/0.25.0
• closes Update context.tf #41

[korenyoni]

/test all

[nitrocode]

/test all