test(W-18772941): test against LLM Gateway

[mdonnalley]

What does this PR do?

Adds a script (yarn test:llmg) to test that tools are successfully invoked across multiple LLMs

Developers will need to set SF_LLMG_API_KEY to the api key, which will be stored in 1password

Developers will also need a llmg-test.yml (which is gitignored) to tell the test which models and prompts to use. For example,

models:
  - llmgateway__OpenAIGPT35Turbo_01_25
  - llmgateway__OpenAIGPT4OmniMini
  - llmgateway__BedrockAnthropicClaude4Sonnet

prompts:
  - What's my salesforce username?
  - List all my orgs
  # send multiple messages to the LLM
  - - I am a Salesforce developer. My current working directory is ~/my-project. My current org is [email protected].
      - Deploy my project

At this point the script is meant to be used during development to help write tool descriptions and parameters that are effective across multiple LLMs.

In the future we could possibly leverage this to write regression tests (although that would be expensive!)

What issues does this PR fix or reference?

@W-18772941@