Support for changing group labels

[Shaked]

When creating a new group or maintaining an existing one, there's a need to decide which type of group we would like to support. GCP allows the usage of two: DISCUSSION and SECURITY. Currently, it's not possible to decide which labels to use and GCP doesn't allow removing existing labels, therefore once a group is marked with either of the above, there's no way to apply terraform anymore.

This PR helps overcome the issue of existing labels and also exposes a new feature - support to add a security group.

Usage example:

module "group" {
  for_each     = { for group in local.group_members : group.group_name => group }
  source       = "terraform-google-modules/group/google"
  version      = "~> 0.1"
  customer_id  = local.customer_id
  id           = "${each.value.group_name}@${local.google_domain}"
  display_name = each.value.display_name
  description  = each.value.description
  members      = each.value.members
  label_keys = [
    "default",
    "security",
  ]
}

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[comment-bot-dev]

Thanks for the PR! 🚀 Unfortunately it looks like some of our CI checks failed. See the Contributing Guide for details.

• ⚠️check_documentation The documentation needs to be regenerated. Please run make generate_docs.

  Checking for documentation generation
  diff -r '--exclude=.terraform' '--exclude=.kitchen' '--exclude=.git' '--exclude=autogen' '--exclude=*.tfvars' /workspace/README.md /tmp/tmp.DYYrdgeK6N/generate_docs/workspace/README.md
  43a44
  > | label\_keys | Labels to apply to the group. Currently only 'default' is supported | `list` | <pre>[<br>  "default"<br>]</pre> | no |
  Error: Documentation generation has not been run, please run the
  'make docker_generate_docs' command and commit the above changes.

[github-actions[bot]]

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