Update HA language on the Overview page

[angellk]

On the Dapr.io Overview page, the following language is misleading and may suggest there is a hard dependency on Hashicorp Consul service for HA mode.

The Dapr control plane services can be deployed in high availability (HA) mode to clusters of physical or virtual machines in production. In the diagram below, the Actor Placement and security Sentry services are started on three different VMs to provide HA control plane. In order to provide name resolution using DNS for the applications running in the cluster, Dapr uses Hashicorp Consul service, also running in HA mode.

xref: cncf/toc#1354