feat: migrate legacy docs (#1568)

apps/next/src/content/docs/llamaindex/guide/meta.json

apps/next/src/content/docs/llamaindex/index.mdx

apps/next/src/content/docs/llamaindex/meta.json

.../next/src/content/docs/llamaindex/modules/agent/index.mdx

.../next/src/content/docs/llamaindex/modules/chat_engine.mdx

apps/next/src/content/docs/llamaindex/modules/data_index.mdx

.../content/docs/llamaindex/modules/data_loaders/discord.mdx

...rc/content/docs/llamaindex/modules/data_loaders/index.mdx

...src/content/docs/llamaindex/modules/data_loaders/json.mdx

...cs/llamaindex/modules/data_loaders/llama_parse/images.mdx

...ocs/llamaindex/modules/data_loaders/llama_parse/index.mdx

...llamaindex/modules/data_loaders/llama_parse/json_mode.mdx

...docs/llamaindex/modules/data_stores/chat_stores/index.mdx

.../docs/llamaindex/modules/data_stores/doc_stores/index.mdx

...src/content/docs/llamaindex/modules/data_stores/index.mdx

...ocs/llamaindex/modules/data_stores/index_stores/index.mdx

...t/docs/llamaindex/modules/data_stores/kv_stores/index.mdx

...cs/llamaindex/modules/data_stores/vector_stores/index.mdx

...s/llamaindex/modules/data_stores/vector_stores/qdrant.mdx

...ent/docs/llamaindex/modules/documents_and_nodes/index.mdx