Please allow searchContent config to take custom frontmatter fields instead of just 'title'

[clairep94]

Is your feature request related to a problem? Please describe

I am working on a public API docs site for my company which uses Nuxt Content md files to create all the page contents.
I want to be able to search the docs using custom frontmatter properties, instead of just 'title'.

Describe the solution you'd like

content: {
    experimental: {
      search: {
        options: {
          fields: ['title', 'titles', 'customFrontmatterField'], // I want to be able to add a custom front matter property name here
          storeFields: ['title', 'titles'],
          searchOptions: {
            prefix: true,
            fuzzy: 0.2,
            boost: {
              title: 4,
              content: 2,
              titles: 1
            }
          }
        }
      },
      clientDB: true,
    }
  }, 

Describe alternatives you've considered

I can search by content, but there is some stuff in frontmatter that are not in the content. For example tags

Additional context