feat: Build files nodes for GraphCMS image assets

[ynnoj]

Uses createRemoteFileNode to build local file nodes for GraphCMS images.

Can be used with gatsby-image etc.

This features is opt in, must be enabled in gatsby-config.js:

{
  resolve: 'gatsby-source-graphcms',
  options: {
    downloadLocalImages: true
  }
}

[github-actions[bot]]

:tada: This PR is included in version 0.1.0-next.1 :tada:

The release is available on:

• npm package (@next dist-tag)
• GitHub release

Your semantic-release bot :package::rocket:

[github-actions[bot]]

:tada: This PR is included in version 1.1.0-next.1 :tada:

The release is available on:

• npm package (@next dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: