[FEATURE]: Register model under multiple names for LoRA

[grahamking]

Feature request

A worker should be able to 1. register itself under multiple names, and 2. the used name should be passed on to the worker. It will use the name to decide which LoRA to use.

Thoughts on 1:

• register_llm could accept either a string or an array of string
• In Rust we put the handler in the map multiple times. The handler will probably be in an Arc

Thoughts on 2:

• If we don't do pre-processing the worker should already get the model name, we pass on the request.
• If we do pre-processing, check that the model name ends up in the JSON that we send the model, with the token ids.

[grahamking]

Some prep work here: #2349

[grahamking]

Pass the model name to the worker here: #2397

[grahamking]

The LoRA adapters are not all available to the worker on startup. Instead of changing register_llm, the worker will call it multiple times. That means register_llm itself does not need to change, but we need to change elsewhere, see #2418

[grahamking]

Completed.