fix: move mongodb to examples/

apps/mongodb/CHANGELOG.md

apps/mongodb/package.json

examples/data/tinytweets.json

examples/mongodb/1_import.ts

examples/mongodb/2_load_and_index.ts

examples/mongodb/3_query.ts

examples/mongodb/README.md

examples/mongodb/docs/1_signup.png

examples/mongodb/docs/2_connection_string.png

examples/mongodb/docs/3_vectors_in_db.png

examples/mongodb/docs/4_search_tab.png

examples/mongodb/docs/5_json_editor.png

examples/mongodb/docs/7_index_created.png

examples/package.json

pnpm-lock.yaml