feat: make use of pre-commit's native golang support for terraform-docs

As noted in #13, using pre-commit's native golang support for running terraform-docs provides the ability for renovate to auto-update the version as required. It also allows renovate to run terraform-docs whenever a template is updated.

Hold off on moving tflint for the moment since tflint makes use of a custom ruleset plugin which is non-trivial to install via pre-commit.

Tested in gcp-secret-manager via gcp-secret-manager@e663d7b5 and a successful pre-commit job run.

Closes #14 (closed)