docs(influxdb3): Clarify and differentiate "none" vs zero retention periods

[jstirnaman]

Goal

Clarify monolith database and table retention period behaviors for supported values.

Tasks

1. Clarify behavior when retention period is "none". Provide example.
2. Clarify behavior when retention period is 0 in the docs. Provide example.
3. Differentiate "none" vs 0

Slack Message