Add an endpoint to the SDK where metrics can be retrieved adhoc

[sgalsaleh]

What this PR does / why we need it:

Adds an endpoint to the SDK where metrics can be retrieved adhoc to facilitate the KOTS/SDK integration and telemetry reconciliation.

Which issue(s) this PR fixes:

Fixes SC-90703

Special notes for your reviewer:

• Valid license ID:

$ curl -s -H 'Authorization: 2MqOPWspoqXLAIBchNPJA87GOzM' 10.43.103.73:3000/api/v1/app/metrics | jq .
{
  "X-Replicated-AppStatus": "unavailable",
  "X-Replicated-ClusterID": "7262d9de-1a14-417e-bc58-e2f714776f0a",
  "X-Replicated-DownstreamChannelID": "2MqOAm2LeY9gsaqFwczXAoSfRtD",
  "X-Replicated-DownstreamChannelSequence": "69",
  "X-Replicated-InstanceID": "7262d9de-1a14-417e-bc58-e2f714776f0a",
  "X-Replicated-K8sDistribution": "k3s",
  "X-Replicated-K8sVersion": "v1.20.2+k3s1"
}

• Invalid license ID:

$ curl -s -H 'Authorization: invalid' 10.43.103.73:3000/api/v1/app/metrics | jq .
{
  "error": "license ID is not valid",
  "success": false
}

• No authorization header / license ID:

$ curl -s 10.43.103.73:3000/api/v1/app/metrics | jq .
{
  "error": "missing authorization header",
  "success": false
}

Steps to reproduce

Does this PR introduce a user-facing change?

NONE

Does this PR require documentation?

NONE