feat: add base evaluator and correctness evaluator (#559)

.changeset/famous-pugs-join.md

.changeset/sharp-ducks-clap.md

apps/docs/docs/modules/evaluation/_category_.yml

apps/docs/docs/modules/evaluation/index.md

apps/docs/docs/modules/evaluation/modules/_category_.yml

apps/docs/docs/modules/evaluation/modules/correctness.md

apps/docs/docs/modules/evaluation/modules/faithfulness.md

apps/docs/docs/modules/evaluation/modules/relevancy.md

examples/evaluation/correctness.ts

examples/evaluation/faithfulness.ts

examples/evaluation/relevancy.ts

packages/core/src/evaluation/Correctness.ts

packages/core/src/evaluation/Faithfulness.ts

packages/core/src/evaluation/Relevancy.ts

packages/core/src/evaluation/index.ts

packages/core/src/evaluation/prompts.ts

packages/core/src/evaluation/types.ts

packages/core/src/evaluation/utils.ts

packages/core/src/index.ts

packages/core/src/indices/summary/index.ts