cli: add prometheus deployment and metrics integration to demo preset

[david-yu]

Changes proposed in this PR:

• enables metrics on agents, gateway, and metrics merging
• enables prometheus for deployment through Helm config

How I've tested this PR:

Installed using this branch of consul-k8s

~/projects/consul-k8s/cli main*
❯ consul-k8s install -preset=demo

==> Pre-Install Checks
No existing installations found.
 ✓ No previous persistent volume claims found
 ✓ No previous secrets found

==> Consul Installation Summary
    Installation name: consul
    Namespace: consul
    Overrides:
    connectInject:
      enabled: true
      metrics:
        defaultEnableMerging: true
        defaultEnabled: true
        enableGatewayMetrics: true
    global:
      metrics:
        enableAgentMetrics: true
        enabled: true
      name: consul
    prometheus:
      enabled: true
    server:
      bootstrapExpect: 1
      replicas: 1
    ui:
      enabled: true
    service:
        enabled: true

    Proceed with installation? (y/N) y

==> Running Installation
 ✓ Downloaded charts
 --> creating 1 resource(s)
 --> creating 33 resource(s)
 --> beginning wait for 33 resources with timeout of 10m0s
 --> DaemonSet is not ready: consul/consul. 2 out of 3 expected pods have been scheduled
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 --> DaemonSet is not ready: consul/consul. 0 out of 2 expected pods are ready
 ✓ Consul installed into namespace "consul"

~/projects/consul-k8s/cli main* 50s
❯ k get pods -n consul
NAME                                                          READY   STATUS    RESTARTS   AGE
consul-6f8pt                                                  1/1     Running   0          76s
consul-connect-injector-webhook-deployment-856b578bcf-4f6rj   1/1     Running   0          76s
consul-connect-injector-webhook-deployment-856b578bcf-pl5tg   1/1     Running   0          76s
consul-p4ncd                                                  1/1     Running   0          76s
consul-server-0                                               1/1     Running   0          75s
consul-webhook-cert-manager-b698db889-nhw77                   1/1     Running   0          76s
consul-xgch8                                                  1/1     Running   0          76s
prometheus-server-c5f9465d-52zrl                              2/2     Running   0          76s

Deployed HashiCups from https://github.com/hashicorp/learn-consul-kubernetes/tree/main/layer7-observability and simulated some traffic.

How I expect reviewers to test this PR:

Checklist:

• Tests added
• CHANGELOG entry added

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

[thisisnotashwin]

💥

[ndhanushkodi]