docs: update exa search (#24861)

- [x] **PR title**: "docs: changed example for Exa search retriever
usage"

- [x] **PR message**:
- **Description:** Changed Exa integration doc at
`docs/docs/integrations/tools/exa_search.ipynb` to better reflect simple
Exa use case
- **Issue:** move toward more canonical use of Exa method
(`search_and_contents` rather than just `search`)
    - **Dependencies:** no dependencies; docs only change
    - **Twitter handle:** n/a - small change

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17. - will do

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Co-authored-by: Erick Friis <[email protected]>