Adding capability to configure private Route53 domains

[chrislovecnm]

Description

At times a user will want to configure private Route53 domains. This introduces the capability to set a flag and have terraform create the private Route53 DNS entries.

This feature is useful to configure such things as split DNS and also allow for private DNS entries for such things as nexus and chartmuseum.

• [X] Change is code complete and matches issue description.
• [ ] Change is covered by existing or new tests.
• [X] Readme is updated
• [ ] jx-docs (https://jenkins-x.io/docs/install-setup/installing/create-cluster/eks/) are updated

Notes for reviewers

I have not checked the use case where we are creating the VPC itself. How would I get the vpc id then?

Which issue this PR fixes

fixes #349

Release notes

New flag added to allow for the create a private Route53 domain. Set create_and_configure_private_subdomain to true and this module will create and manage the private domain.

[chrislovecnm]

/ok-to-test

[chrislovecnm]

I think I have a bug with the for_each, when we don't want to create the associated vpns