Support Cluster Peering with Consul Template

[Esity]

Currently, Consul Template supports querying across federation links to other datacenters but has no docs and appears to not support querying services from peering connections which seems silly

consul-template/docs/templating-language.md

Lines 200 to 230 in 2d446f0

	### `datacenters`
	Query [Consul][consul] for all datacenters in its catalog.
	```golang
	{{ datacenters }}
	```
	For example:
	```golang
	{{ range datacenters }}
	{{ . }}{{ end }}
	```
	renders
	```text
	dc1
	dc2
	```
	An optional boolean can be specified which instructs Consul Template to ignore
	datacenters which are inaccessible or do not have a current leader. Enabling
	this option requires an O(N+1) operation and therefore is not recommended in
	environments where performance is a factor.
	```golang
	// Ignores datacenters which are inaccessible
	{{ datacenters true }}
	```

I don't see a good reason on why we wouldn't add this in as a supported thing considering federation is going away
Example PR talking about querying consul via DNS for peering
https://github.com/hashicorp/consul/blob/3332f63c4c00592e186843df85df9a5d0241cf7b/website/content/docs/services/discovery/dns-static-lookups.mdx#L102-L110

[blake]

@Esity Support for listing peers and querying services from peers was implemented in #1822 and #1869, and is available in the recent releases of Consul template.