Description:

Adds support for Consul's /v1/imported-services API endpoint, enabling consul-template to query and template services imported from other partitions in Consul Enterprise

Testing Setps:

1. Create the setup with consul server agent, 2 partitions with consul client agen running on each partition, register services in each partition, then export services from one partition to another.
2. imported-services.ctmpl

=== Imported Services for Downstream Partition ===

{{- range importedServices "downstream" }}
Service: {{ .Service }}
  Namespace: {{ .Namespace }}
  Source Partition: {{ .SourcePartition }}
{{- end }}

3. consul-template -consul-addr="http://127.0.0.1:8500" -template="imported-result.txt" -once
4. Result: imported-result.txt

=== Imported Services for Downstream Partition ===
Service: payments
  Namespace: default
  Source Partition: upstream

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.

• If applicable, I've documented the impact of any changes to security controls.

  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.