feat(reranker): cohere reranker (#535)

.changeset/olive-wolves-own.md

apps/docs/docs/modules/data_loader.mdx

apps/docs/docs/modules/embedding.md

apps/docs/docs/modules/node_parser.md

apps/docs/docs/modules/node_postprocessors/_category_.yml

.../docs/docs/modules/node_postprocessors/cohere_reranker.md

apps/docs/docs/modules/node_postprocessors/index.md

examples/rerankers/CohereReranker.ts

packages/core/package.json

packages/core/src/engines/chat/DefaultContextGenerator.ts

packages/core/src/engines/query/RetrieverQueryEngine.ts

...re/src/postprocessors/MetadataReplacementPostProcessor.ts

packages/core/src/postprocessors/SimilarityPostprocessor.ts

packages/core/src/postprocessors/index.ts

packages/core/src/postprocessors/rerankers/CohereRerank.ts

packages/core/src/postprocessors/rerankers/index.ts

packages/core/src/postprocessors/types.ts

...s/postprocessors/MetadataReplacementPostProcessor.test.ts

pnpm-lock.yaml