Updating the example for current software versions

[kellyhair]

Changes to aws-kms-unseal-ha:

• Updated versions.tf to required Terraform 0.13 or greater.
• Vault updated to 1.6.3. URL added to the variables.tf.
• Consul updated from 1.0.0 to 1.9.4. Additionally, extrapolated OS & CPU architecture in the userdata.tpl.
• Moved from Ubuntu 16.04 (Xenial) LTS to 20.04 (Focal) LTS.
• Updated README.md to update the unseal instructions.

Changes to aws-kms-unseal:

• Added versions.tf file; set required version of Terraform to 0.13.
• Bumped version of Vault to 1.6.3 from 1.6.0.

Notes:

Tested both plans (aws-kms-unseal & aws-kms-unseal-ha) with Terraform v0.13.0 and v0.14.8. Terraform v0.14.8 was the most recent as of commits & PR.

[hashicorp-cla]

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[kellyhair]

I noticed that I left some commented lines in. Will clean up & resubmit.

[kellyhair]

Updated files; reopening

[yhyakuna]

@kellyhair Could you please review and agree to CLA?