[CI] Use different consul versions (release/1.2.0)

[curtbushko]

Changes proposed in this PR:

• this is a release branch version of [CI] Use different consul versions #2342
• add/update make targets to do the following:

$ make consul-version
docker.mirror.hashicorp.services/hashicorppreview/consul:1.16-dev

$ make consul-enterprise-version
docker.mirror.hashicorp.services/hashicorppreview/consul-enterprise:1.16-dev

This way we can use this in the pipelines to make sure that the correct consul version is passed into the tests.

How I've tested this PR:

How I expect reviewers to test this PR:

Checklist:

• Tests added
• CHANGELOG entry added

  HashiCorp engineers only, community PRs should not add a changelog entry.
  Entries should use present tense (e.g. Add support for...)