feat(plugin-seo): export fields from plugin seo so that they can be imported freely in a collection fields config

[paulpopus]

Exports the fields from the SEO plugin so that they can be used anywhere inside a collection, new exports:

import { MetaDescriptionField, MetaImageField, MetaTitleField, OverviewField, PreviewField } from '@payloadcms/plugin-seo/fields'

// Used as fields
MetaImageField({
  relationTo: 'media',
  hasGenerateFn: true,
})

MetaDescriptionField({
  hasGenerateFn: true,
})

MetaTitleField({
  hasGenerateFn: true,
})

PreviewField({
  hasGenerateFn: true,
  titlePath: 'meta.title',
  descriptionPath: 'meta.description',
})

OverviewField({
  titlePath: 'meta.title',
  descriptionPath: 'meta.description',
  imagePath: 'meta.image',
})

[jacobsfletch]

IMO these exports need to be appended with Field, i.e. MetaImageField

[jacobsfletch]

We also need docs for this and all other plugin changes, i.e. the new function overrides pattern. Those are under the /docs/plugins/seo directory.