[ENHANCEMENT] Pre-warming models API Endpoint

[vicilliar]

Describe the solution you'd like
Currently the only way to pre-warm models is on marqo startup, with the env var MARQO_MODELS_TO_PRELOAD

It would be useful to have an API Endpoint to load and pre-warm models while marqo is already up and running. For example, it could be something like @app.post("/models/pre-warm")