Add support for IAM access group template

[ocofaigh]

Add a submodule (similar to terraform-ibm-modules/terraform-ibm-iam-account-settings#424) for creating access group template for enterprise

An "enterprise" example should be added which calls the new submodule (similar to this) and a test should be added to run the example (NOTE to core team - the default apikey will need to be updated in this repo so that the test will run on our enterprise account)

[gmzcarlos]

Created PR #316