Reorganise _config - move run-specific items out of plugins and into run

[leondz]

Summary

Move the following from _config.plugins to _config.run:

• model_type
• model_name
• extended_detectors
• probe_spec
• detector_spec
• buff_spec

Test at least that:

• they're present in _config.run
• they're correctly populated in _config.run
• they're absent in _config.plugins
• each one is picked up correctly in at least one place

Basic example

the following config becomes valid:

---
run:
  model_name: openai
  probe_spec: encoding
plugins:
  generators:
    openai:
      OpenAIGenerator:
        name: gpt-4

Motivation

Items that shape the current run, and affect what is tested for, must be placed in _config.run. The contents of _config.plugins specify how plugins run, if they run. _config.run is about orchestration. _config.plugins is about helping individual plugins and plugin families execute.