Prevent big cache file for yaml.

[comfuture]

Is your feature request related to a problem? Please describe

When I tried to serve hundreds of yaml files in a static build using nuxt content, I found that it created a very big .output/public/cache.XXXXX.json file.

Describe the solution you'd like

Unlike a markdown file, where only the frontmatter is indexed, having all yaml fields cached and growing to several megabytes is not the desired effect.
�It should be able to control which fields are included (or excluded) in the cache.

Describe alternatives you've considered

I think there should be an option to specify fields that you want to index (separate from search).

Additional context