feat: update metadata extractor to use prompt template (#1338)

.changeset/plenty-wolves-smile.md

packages/core/src/prompts/index.ts

packages/core/src/prompts/prompt.ts

packages/llamaindex/src/extractors/MetadataExtractors.ts

packages/llamaindex/src/extractors/prompts.ts

packages/llamaindex/src/extractors/types.ts

packages/llamaindex/tests/MetadataExtractors.test.ts