Description: This PR changes the import section of the
`PydanticOutputParser` notebook.
* Import from `langchain.pydantic_v1` instead of `pydantic`
* Remove unused imports
Issue: running the notebook as written, when pydantic v2 is installed,
results in the following:
```python
PydanticDeprecatedSince20: Pydantic V1 style `@validator` validators are deprecated. You should migrate to Pydantic V2 style `@field_validator` validators, see the migration guide for more details. Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.3/migration/
```
[...]
```python
PydanticUserError: The `field` and `config` parameters are not available in Pydantic V2, please use the `info` parameter instead.
For further information visit https://errors.pydantic.dev/2.3/u/validator-field-config-info
```
Various improvements to the Model I/O section of the documentation
- Changed "Chat Model" to "chat model" in a few spots for internal
consistency
- Minor spelling & grammar fixes to improve readability & comprehension