chore(gatsby): Make plugins in PluginOptions type optional

[LekoArts]

Description

So I've ran into this while I defined a interface CustomPluginOptions extends PluginOptions in a plugin. I extend the PluginOptions from gatsby here so that I can use it in the gatsby-config and in the gatsby-node APIs.

But with plugins being required TS complained that my plugin didn't define plugins.

import type { GatsbyConfig, PluginRef } from "gatsby"
import type { CustomPluginOptions } from "plugin"

const config: GatsbyConfig = {
  plugins: [
    {
      resolve: `plugin`,
      options: {
        api_key: process.env.api_key,
        plugins: [], // This here is necessary to add at the moment
      } as CustomPluginOptions,
    },
  ] as PluginRef[],
}

export default config

I know, we set this by default, but for using this type in 3rd party packages it's annoying

[pieh]

I think you want to extend IPluginRefOptions, not PluginOptions for gatsby-config inputs at least. First one are types for the input (with plugins being optional), PluginOptions will be values passed to our APIs and plugins will always be an array there