gatsby-config.js有什么作用？

// gatsby-config.js
module.exports = {
  siteMetadata: {
    title: `Gatsby`,
    siteUrl: `https://www.gatsbyjs.com`,
    description: `Blazing fast modern site generator for React`,
  },
  plugins: [
    `gatsby-transform-plugin`,
    {
      resolve: `gatsby-plugin-name`,
      options: {
        optionA: true,
        optionB: `Another option`,
      },
    },
  ],
  flags: {
    QUERY_ON_DEMAND: true,
  },
  pathPrefix: `/blog`,
  proxy: {
    prefix: "/api",
    url: "http://examplesite.com/api/",
  },
}