Change IAM execution policy condition to require consul_ca_cert_arn instead of tls

[jcolemorrison]

Changes proposed in this PR:

• Changes the condition in the IAM execution policy on whether the "secretsmanager:GetSecretValue" statement is added to the existence of the var.consul_ca_cert_arn. This makes it so that TLS can be enabled without passing that value and uses the logic used for the other statements in that IAM policy.

How I've tested this PR:

How I expect reviewers to test this PR:

Checklist:

• [ ] Tests added
• [ ] CHANGELOG entry added

[jcolemorrison]

Whoops, meant to match that. Changed it around!