feat: support cortex engines init command

[louis-jan]

Describe Your Changes

• This is to support cortex engines init command, for the case that support engines ahead of time, eg docker build.

// Llama.cpp engine
cortex engines init cortex.llamacpp

// ONNX engine
cortex engines init cortex.onnx

// Tensorrt-LLM engine
cortex engines init cortex.tensorrt-llm

// DO NOT INIT REMOTE ENGINES

Fixes Issues

• Closes feat: cortex should support engines init to reinit engines manually #809

Self Checklist

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