docs(model): update examples to match the new interface with kwargs

[mkmeral]

Description

Add **kwargs to necessary places as a follow up on the interface changes.

strands-agents/sdk-python#413

Type of Change

• Content update/revision

Motivation and Context

There were backwards compatible changes, as a result docs are incorrect.

Areas Affected

Custom models

Screenshots

Checklist

• [ x] I have read the CONTRIBUTING document
• [x ] My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• Links in the documentation are valid and working
• Images/diagrams are properly sized and formatted
• [x ] All new and existing tests pass

Additional Notes

None

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.