Populate primary dc flag for APIGW controller in secondary federated dc

[nathancoleman]

Note This is the third of three in the chain of PRs required to get Consul API Gateway working in a secondary federated datacenter:

• https://github.com/hashicorp/consul-k8s/pull/1481
• https://github.com/hashicorp/consul-api-gateway/pull/368
• https://github.com/hashicorp/consul-k8s/pull/1511

Changes proposed in this PR:

• When deployed into a secondary datacenter with federation enabled, populate the primary-datacenter flag added to Consul API Gateway's controller in https://github.com/hashicorp/consul-api-gateway/pull/368

How I've tested this PR: Install a federated setup as described in this guide, making sure that API Gateway is enabled in both datacenters and using the latest build from main:

apiGateway:
  enabled: true
  image: "hashicorppreview/consul-api-gateway:0.5-dev"

Once completed, install a Gateway into the secondated datacenter and ensure it works. This guide sufficiently exercises this behavior.

How I expect reviewers to test this PR: See above

Checklist:

• [x] Tests added
• [x] CHANGELOG entry added

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

[manobi]

Are there chances of it to be included in the next release?

[nathancoleman]

@manobi that is my intention