Add `conjur health` command to query component health metrics

[infamousjoeg]

The ability to use the Conjur CLI to receive the health metrics of an appliance is being requested to provide "Ease of Use" to users of the CLI.

Currently, the only way to receive health metrics on appliances is by curling the available API:

curl https://dap_address/health

The preferred command in Conjur CLI would be:

conjur health

Providing the ability to choose output would also be an added bonus:

JSON output: conjur health -o json

STDOUT output (for human consumption): conjur health -o stdout