chore(gatsby-plugin-netlify): add pluginOptionsSchema export

[mfrachet]

Description

Add plugin options schema to gatsby-plugin-netlify.

• The plugin documentation
• Relates to feat(gatsby): plugin option validation #27242

Here are the potential options to pass to the plugin:

plugins: [
  {
    resolve: `gatsby-plugin-netlify`,
    options: {
      headers: {}, // option to add more headers. `Link` headers are transformed by the below criteria
      allPageHeaders: [], // option to add headers for all pages. `Link` headers are transformed by the below criteria
      mergeSecurityHeaders: true, // boolean to turn off the default security headers
      mergeLinkHeaders: true, // boolean to turn off the default gatsby js headers
      mergeCachingHeaders: true, // boolean to turn off the default caching headers
      transformHeaders: (headers, path) => headers, // optional transform for manipulating headers under each path (e.g.sorting), etc.
      generateMatchPathRewrites: true, // boolean to turn off automatic creation of redirect rules for client only paths
    },
  },
]

Notes:

• headers is a specific netlify type corresponding to { [key: string]: Array<string> } (See details)
• transformHeaders is a function, but I didn't find a way to tell Joi about the return type of that function. In that scenario, the return type should be of type Netlify Headers (see previous bullet)

[mxstbr]

Overall looks fantastic but I'd love to see descriptions added!

[mxstbr]

Fantastic! 💯