feat: vllm support (#1468)

.changeset/pink-dolls-destroy.md

examples/vllm.ts

packages/llamaindex/package.json

packages/llamaindex/src/llm/index.ts

packages/providers/vllm/package.json

packages/providers/vllm/src/index.ts

packages/providers/vllm/src/llm.ts

packages/providers/vllm/tsconfig.json

pnpm-lock.yaml

tsconfig.json