feat: add nextjs plugin for `llamaindex` (#824)

.changeset/warm-papayas-wait.md

README.md

packages/core/e2e/examples/nextjs-agent/next.config.mjs

...ges/core/e2e/examples/nextjs-edge-runtime/next.config.mjs

.../e2e/examples/nextjs-edge-runtime/src/app/page.module.css

...es/core/e2e/examples/nextjs-edge-runtime/src/app/page.tsx

...es/core/e2e/examples/nextjs-edge-runtime/src/utils/llm.ts

packages/core/e2e/examples/nextjs-edge-runtime/tsconfig.json

packages/core/src/embeddings/ClipEmbedding.ts

packages/core/src/embeddings/HuggingFaceEmbedding.ts

packages/core/src/internal/deps/transformers.ts

packages/core/src/next.ts