feat: support Together AI (#373)

examples/together-ai.ts

packages/core/src/embeddings/OpenAIEmbedding.ts

packages/core/src/embeddings/index.ts

packages/core/src/embeddings/together.ts

packages/core/src/llm/LLM.ts

packages/core/src/llm/index.ts

packages/core/src/llm/together.ts

packages/eslint-config-custom/index.js