Document recommendations for naming conventions for slugs in theme.json when configuring preset settings

[DaisyOlsen]

What is the new page you are requesting?

Continuation of #563

Add more detail about recommendations for using more semantic slugs This page should be written from a high level since slug names are used across all presets in theme.json.

Ideally, mentions of creating preset slugs in theme.json can link out to this page to support more specific recommendations for individual preset settings.

How will this new page help you?

Begin to provide information about best practices for naming conventions used in theme.json across presets to encourage consistent standards across block themes.

[github-actions[bot]]

Heads up @kafleg @carolinan @TeBenachi - the "themes" label was applied to this issue.

[zzap]

Heads up @WordPress/docs-issues-coordinators, we have a new issue open. Time to use 'em labels.