feat: pruning conversation conversation manager docs

[roeetal]

Description

Implement documentation for pruning conversation manager to prune messages in the agent conversation history. See PR.

Type of Change

• New content addition
• Content update/revision
• Structure/organization improvement
• Typo/formatting fix
• Bug fix
• Other (please describe):

New content addition

Motivation and Context

Provides documentation for a mechanism to prune conversation messages.

Areas Affected

• docs/user-guide/concepts/agents/conversation-management.md
• mkdocs.yml
• docs/examples/python/conversation_pruning.md
• docs/examples/python/conversation_pruning.py
• docs/user-guide/concepts/agents/conversation-pruning.md

Screenshots

Checklist

• I have read the CONTRIBUTING document
• 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
• All new and existing tests pass

Additional Notes

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