Add vault enterprise support

[dannyibishev]

• Adds condition for terraform enterprise, if a license is provided (via a new secret manager secret), then the user data script will install the terraform enterprise binary and export the required vault variable before the service is started. - Closes #45
• Health check improvements. - Closes #44
• Bumped up the AWS provider requirements to >= 4.0.0.
• Replaced the aws_autoscaling_group tag method. tags is deprecated. The new recommended way to specify tags is by using the tag block

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Update (7 September 2022)

I have added a lot more than I would have liked for my use-case. Therefore, I will leave the owners to decide whether they want to make tweaks to make it acceptable for this module, or if they want to close it.

Here are a few other changes that were made in order to support terraform enterprise (for our usecase) using the integrated storage architecture.

• DNS autoscaling. This was added for the node to node communication. I needed a way for my nodes to find each other and trust each other using mTLS (as recommended by best practices) - To save time and keep complexity low, I ended up using another third party module to achieve this. Basically, the lifecycle policy on the ASG creates and removes records on the private route53 hosted zone.
• Added the ability to specify KMS administrators.
• Encrypted most of the essential resources with the KMS key and added the required policies to achieve this.
• replaced the ASG and Launch Template resource with that of a third party module.
• Added trust for the self managed CA certificate to the certificate chain on the nodes.

I'd also suggest a git rebase is done to tidy up the commit names and splice together test commits so there's less noise

[troyready]

Hi @dannyibishev . Sorry for not responding sooner here. Very much appreciate the contributions you've done.

I'm going to close this out, but I'd encourage anyone interested in any of its features to pick it up and open a separate issue to explore it. The only technical/procedural note I'll make is that we currently have a separate module for deploying Vault Enterprise, so anyone picking up the same features should split them between the modules as appropriate.

[dannyibishev]

@troyready Thanks for looking into this.

May I suggest you add labels to the enterprise vault module repository as I could not find it easily when I first started looking into this.