Enable Confluent Cloud API authentication using Confluent Cloud API Keys

[mcohen75]

The Confluent Cloud API supports authentication via API keys. At Indeed we use Terraform to manage our Confluent Cloud infrastructure. Authentication using API keys is preferred over username and password authentication.

Confluent Cloud API documentation for using API keys to authenticate:
https://confluent.cloud/api/docs#section/Authentication

Note that Confluent Cloud supports two types of API keys, cluster and cloud.

Cloud API Keys - These grant access to the Confluent Cloud Control Plane APIs, such as for Provisioning and Metrics integrations.
Cluster API Keys - These grant access to a single Confluent cluster, such as a specific Kafka or Schema Registry cluster.

I created an issue against the go-client-confluent-cloud as it appears the client does not yet support API Key based authentication:
cgroschupp/go-client-confluent-cloud#13