This custom TFLint image includes the UIS DevOps custom tflint ruleset.
This change does not impact existing repositories by default but allows
them to opt in to the custom ruleset if desired.

The default TFLint arguments are now defined in a variable, allowing
repositories to override them as needed. For example, reusable Terraform
modules may want to enable the `terraform_standard_module_structure` rule
and can now do so by overriding the default arguments.

We would like to start using tflint on our reusable Terraform Module repos. Therefore, we're removing the TFLINT_DISABLED variable from this template.

feat(tflint): use custom tflint image

See merge request !129