Document RedisVL exception hierarchy and error handling patterns

[tylerhutcherson]

Summary

Document RedisVL exception hierarchy and practical error handling patterns.

Level: Beginner

Current State

• Custom exceptions are defined in redisvl/exceptions.py.
• Documentation does not currently consolidate exception guidance in one discoverable place.

Proposed Change

• Add an API docs page for exceptions.
• Add user-facing guidance for common error categories and recommended handling.
• Include concise try/except examples for schema validation and query failures.

Definition of Done

• Exception docs are present and discoverable in generated docs.
• make docs-build passes.
• Examples align with current exception classes.

Out of Scope

• Redesigning exception class hierarchy.