Add support for recursor flag

[m-yosefpor]

Fixes: #984

Changes proposed in this PR:

• Add support for -recursor flag (https://www.consul.io/docs/agent/options#_recursor)

How I've tested this PR: Yes, provided in next section.

How I expect reviewers to test this PR:

1. Default value should not change any manifests. i.e.

global:
    recursors: null

2. Setting a list of IP addresses, will provide the flag to server and clients, and user should be able to resolve queries recursively.

global:
   recursors:
   - 8.8.8.8
   - 1.1.1.1

Looking up a domain outside of consul domain in agents, and servers should return IP address:

$ kubectl exec consul-74tmn --  nslookup google.com localhost:8600
Server:         localhost:8600
Address:        [::1]:8600

Name:   google.com
Address: 142.251.37.14

Non-authoritative answer:
Name:   google.com
Address: 2a00:1450:400e:808::200e

$ kubectl exec consul-server-0 -- nslookup google.com localhost:8600
Server:         localhost:8600
Address:        [::1]:8600

Name:   google.com
Address: 142.251.37.14

Non-authoritative answer:
Name:   google.com
Address: 2a00:1450:400e:808::200e

Checklist:

• Bats tests added
• CHANGELOG entry added (HashiCorp engineers only, community PRs should not add a changelog entry)

[hashicorp-cla]

All committers have signed the CLA.

[lkysow]

Looks great! Just a couple small suggestions.

[m-yosefpor]

@lkysow Thanks for your review. Suggestions applied.