TS SDK: generic LLM config support

[spichen]

TypeScript port of oracle#147.

LlmConfig was abstract-only before. Now it's a real component you can use directly — handy when none of the specific subclasses fit your setup:

createLlmConfig({
  name: "my-llm",
  modelId: "gpt-4o",
  provider: "openai",
  apiProvider: "openai",
})

Also added: GeminiConfig (AI Studio + Vertex AI), RetryPolicy on all LLM types, TLS cert fields on the OpenAI-compatible family, and XAI to ModelProvider for OCI.

Fields implied by componentType (like provider: "openai" on OpenAiConfig) are excluded from serialized output, matching Python SDK behavior.