Update istio installation instructions

[evie-lau]

The Istio site mentions that helm installation is being deprecated.

Also the ibm charts for Istio are a little outdated.

Instructions page to update: https://github.com/ibm-cloud-architecture/refarch-cloudnative-kubernetes/blob/microprofile/docs/istio.md
Recommended way to install Istio: https://istio.io/docs/setup/getting-started/

[phemankita]

@kevinwlau @dshimo Are you working on updating the Istio instructions ?

[evie-lau]

neither of us are working on this right now, as we've been pulled into other projects.