feat: support cortex configs and engines commands

[louis-jan]

Describe Your Changes

• This PR is to add new Cortex commands

// Get all configs
cortex configs list

// Get a config
cortex configs get openai

// Set a config value
cortex configs set -k apiKey -v 'xx-yy' -g openai

// Get all available engines
cortex engines list

// Get an engine
cortex engines get openai

API

Fixes Issues

• Closes #
• Closes #

Self Checklist

• Added relevant comments, esp in complex areas
• Updated docs (for bug fixes / features)
• Created issues for follow-up changes or refactoring needed

[louis-jan]

Since this PR, all APIs available at /v1

Also printed out Playground URL