[Docs] PR for Helm install: document how to specify a static load balancer IP

[lizayugabyte]

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[jvigil-yugabyte]

As discussed on slack, it may be good to include an example. Here is an example helm "values overrides" file (saved as values-overrides.yaml):

serviceEndpoints:
  - name: "yb-master-ui"
    app: "yb-master"
    loadBalancerIP: "11.11.11.11"
    type: "LoadBalancer"
    ports:
      http-ui: "7000"
  - name: "yb-tserver-service"
    app: "yb-tserver"
    loadBalancerIP: "22.22.22.22"
    type: "LoadBalancer"
    ports:
      tcp-yql-port: "9042"
      tcp-yedis-port: "6379"
      tcp-ysql-port: "5433"

Then, run the following helm command:

helm install yb-demo ./yugabyte -f values-overrides.yaml

Assuming the user has already reserved the ip addresses (11.11.11.11 and 22.22.22.22), the yb-master-ui and yb-tserver-service will use the pre-determined addresses.